I used to share my girlfriend with my roommate when we were in college. My girlfriend and I were virgins and after a few weeks of dating we had sex. Then a couple of months later my roommate walked in while I was balls deep in my girlfriend. After I pulled out I noticed that he was standing there watching. My girlfriend looked at me and then asked my roommate if he wanted a turn. Of course he did and after he undressed she guided him into her. I stood back and watched as he lost his virginity into her just like I had months before.
After he finished, I reentered her and went for a while until I finished and he took another turn in her. During the night we both did her again and in the morning when I woke up he was doing her again.
We continued having sex with her until we finished college. A year later I asked her to marry me and we set a date for the next summer. My roommate was my best man and he joined us on our wedding night and on our honeymoon. After he moved in with us and we have lived together for over 40 years now. We have four children and believe from their looks that we both fathered two of them.