Do I tell or not?

It was last Summer (2024) August and my family was on Vacation down in Ocean City MD.
I’m Patrick, and I’m 16 almost 17 years old. I’m pretty sure I’m straight but after our Summer vacation I’m now thinking I may be bisexual.
This is my story and I would really appreciate any Normal Advice someone can give me. Thanks.
My family consists of Mom, Dad and two older sisters. 23 & 21 and I’m the youngest.
My 23 year old sister (Kathy) had invited her BF (Jack) on vacation.
My parents are pretty religious so even though they know that Kathy and Jack have already slept together, their beliefs are if your not married, you can not sleep in the same room or bed.
Therefore, Jack ended up staying in my room for the week.
My sisters are very attractive especially Kathy. She’s got enormous tits and a small frame. I could see why Jack was attracted to her. My other sister (Rachel) has great body to and this amazing red hair.
Anyway, it was early in our trip that I got this weird feeling that I’d never experienced before.
Jack and Kathy were in the ocean having fun and just goofing off.
When they had returned to our chairs and blankets, it was very obvious that Kathy must have excited Jack because you could clearly see that Jack was aroused just by looking at his bathing suit. I was embarrassed to look, but that did not stop me, nor my Mother from noticing his package.
As the day wore on, my dad said we should all head back to rinse off before we head out for drinks and dinner.
The house we rented was small and had only 1 full bath and 1/2 bath but it did have an outdoor shower. My mom and dad took the indoor shower and my sisters and Jack and I had the outdoor shower. Both my sisters went first together to save on hot water and time. When they finished they both went inside to get ready. Jack went in next but he held the door open and said are you going to rinse off! I was a bit surprised he had asked that, but I acted like it’s not a big deal and said ya be right there.
So I’m now in the shower with Jack and he nonchalantly drops his bathing suit and begins to soap up and rinse off.
I’m shocked that he’s so relaxed being naked next to me. I’m also very embarrassed to remove my bathing suit because I’m maybe 3-4 inches and Jack is very well hung.
So I just said WTF, and dropped my suit.
Jack acted like it was nothing and just went about his business and pretty much ignored me. But that was not true for me.
I could not stop staring at his penis. It was massive compared to mine and his balls were so big and it swollen, hard to tell.
When Jack was soaping up his cock I could not help but notice he began to get semi hard. It was amazing to see this already large cock get even bigger. When we finished, we went back to our bedroom to change. Jack stayed naked in front of me the entire time we changed.
I also noticed that Jack was going out commando in his shorts.
I went to use the bathroom before we left and I had noticed that I was fully erect and I had precum on the tip of my cock. I could not believe I was aroused by seeing Jack naked.
I wanted to be like Jack, so before we left I quickly went back into our bedroom and removed my boxers and also went commando like Jack.
We hit a few bars on the boardwalk prior to dinner. I was the only one not of drinking age so I just watched them all get buzzed and it was fun to watch.
Kathy was wearing a sundress and her boobs were practically out the top. I could clearly tell Jack was enjoying it, because for whatever reason, I was fixated on him and his penis.
After dinner and another few bars we head home for the night!
Kathy and Rachel are pretty fucked up and they call it a night.
Jack and my dad are on the deck having a beer and I went to bed
The house was very hot even with the windows open. I began to change out of my clothes and remembered that I had no boxers on. As I’m removing my shorts, the door opens and it’s Jack. I’m really embarrassed now. Jack said something like you went free balling didn’t you! I sort of laughed and made lite of it. Jack also undressed and when he removed his shorts he had a semi Hardon!
Jack is completely naked now and gets into bed next to me. I’m debating should I put some pjs on or be like Jack and go naked.
I said fuck it, I wanted to be just like Jack.
I get into bed totally naked and Jack and I are just bullshitting with each other.
Jack is asking me if I noticed some of the hot babes on the Boardwalk this evening. I said ya they were hot, but the real truth was I was checking out the bulge in his shorts. Jack was telling me how Horney he has been because he has not had sex in over a month with my sister because he lives in a different state and this was the first time they had seen each other since the end of summer college classes.
Jack said he was going to jerk off in the outdoor shower but he was not sure how I would have reacted. I told Jack that I too was horney and I also had a hardon this afternoon with precum dripping out. Jack said that’s wild and asked if I came. I said no there was not enough time before dinner. Jack said let’s jerkoff together so we can sleep better.
Jack stood up and started to stroke his cock. OMG it had to be twice as big as mine and thick. I was embarrassed to stroke my tiny cock in front of him. I stood up as well but I was having a hard time getting hard. I think I had stage fright. Jack is still pretty buzzed from all the drinking and he said to me I know what will help.
Jack drops to his knees and in one motion before I could even realize what the fuck is about to happen my cock (all of it) is in his mouth. Jack is sucking my cock and I’ve never had a BJ from a girl nevertheless a boy. I was shocked, but something came over me and I started to get really hard and turned on. Jack kept sucking me and his cock was massive now with precum dripping out the tip.
I tell Jack I’m about to cum and he keeps sucking me like it’s a competition. My legs go weak and I start to spasm. My cock starts to squirt and I pump at least 12-14 times in Jacks mouth. Jack continues to suck and swallow all of my cum. He does not miss a drop. When I’m totally empty, Jack stands up and said, I saw you looking at my cock in the shower and I knew you liked it, so I wanted to thank you for looking. Jack said he liked mine as well. Jack asked if I’d like to return the favor. I was a bit nervous, but I said I would try my best. I got on my knees and took Jack into my mouth. His cock already had precum dripping from it and it tasted salty but good. Jack begins to hold
Me head and starts to thrust more and more. I relaxed my throat as much as I could and before I knew it I had almost all of Jack down my throat. It was amazing. I came off his cock and sucked his balls hard. Jack was moaning and telling me not to stop. I put Jack back in my mouth and suck him down to his balls. I was like out of my mind. My own cock was as hard as a fucking rock as well with more precum leaking out.
Jack grabs the back of my head and his balls tighten up and he begins to whisper “I’m cuming” Jack unloads a months worth of cum down my throat. It had to easily be 4-5 tablespoons of thick cum. It just drained out of his cock for what seemed like minutes. As I’m swallowing all his cum in total amazement, my cock starts to spill a load all over the floor without even being touched. It just kept pumping cum into the floor.
Jack and I went to bed and not a word spoken.
The next morning I wake up and Jack is standing in front of me with his cock next to my mouth. He tells me to drain him completely before he goes for breakfast. I deep throat him to his balls and within 3-4 minutes he is unloading his seed into my stomach. Jack whispers into my ear that I’m his official Cock Sucker because my sister Kathy is not good at it nor does she swallow. I told Jack he can use my mouth anytime he wanted.
Jack must have cumed in my mouth at least 20 times that week. I’m so confused if I should say anything to my sister. It’s sort of cheating but I don’t want my sister to be mad at me either. I’m really at a loss. HELP!