Dancing with the devil
My ex wife and I have been divorced for 10 years. Wasn't a good split. I've been remarried for 7 years. She's been remarried for 3. A week ago I got the most awkward text from her ever. She made small talk first then said she said that she is wanting to have a baby with her husband. I said, "Uh...grats?" She said, "We've been trying for a year and no luck." I said, "What does this have to do with me?" She said, "I want u to get me pregnant." I said, "Like a sperm donation?" She said, "Yep. Exactly! But I want the donation the fun way." I said, "You mean..." She said, "I don't think Mark can get me pregnant. So I thought you and I could have sex since it seems every time you and I had sex I got pregnant." I said, "I'm married Gina!" She said, "I am too. They won't have to know."
So we've had sex 4 times in the past week. Looks like she wants it at least that often until she gets pregnant.
Everybody will know it's your kid. It'll be slow, and dumb, and have a really, really small head like the one you think with.