So I'll try to make this story as short as possible.
A little about me. I'm 26, in law school, and have been dating someone for the past 2 1/2 years.
I grew up in prominent family of a smallish town in the south. The cousins on my dad's side of the family (we are a large family and I have 8 aunts and uncles on each side, so 16 in total) are in groups. There's a group of girls my age, then a group of guys with a couple of girls that are in their early to mid thirties right now. I would be lying if I said I hadn't been attracted to this particular cousin my whole life. Growing up he was just an older cousin I barely talked to. The younger group was always playing outside while the older boys always hung out together. So, while we frequently had family get togethers, the two groups rarely mingled, leaving this particular cousin to seem like a cute mysterious older guy but someone I never formed much of a bond with. It wasn't until I was about 22 and we were working on a project together that he and I formed a friendship. Besides working on the project, when we were stressed out, we'd go to a house that his parents owned in town but rarely stayed at as they were always at their other home that they had had their whole adult lives. There we'd just talk about what was going on in our lives, drink beer, and just be there for each other. By this point he had been married for about 3 1/2 years and had a baby with his wife. He and his wife never really got along, something he frequently talked about, and I just enjoyed his company.
One of those nights we were drinking, and he came and sat on the stool next to me. We were watching a video on his phone when he got a phone call. While he was on the phone he started rubbing the back of my leg while I was standing up next to where he was sitting. I just let him do it while I just kept thinking that it was something i had been waiting on ever since we first started getting close. We got up, because he needed to head back to work. In the doorway between the kitchen and the dining room, I was leaning against the door frame. He hung up the call he was on and he just leaned down and kissed me. So much for him going back to work. I kissed him back and he led me to one of the bedrooms where we proceeded to have some of the best sex I've ever had to this day.
This went on for months with him sometimes coming to my house, other times him going to his parents' house they never used, and a couple of times its happened at his own house. Once when I had slept over after getting drunk with him and his wife the night before. The next morning his wife came into the guest room where I was to see if I was sleeping. I pretended to sleep as I assumed she wanted to invite me to breakfast since that's where she was heading with their daughter and her mom. He woke up later and came into the guest room. It happened another time at his house when his wife was out of town at a concert.
This has happened every few weeks for the last 3 years. I've grown feelings for him, but as he's my first cousin and married with a child I never even told him about my feelings. I don't feel I have to because I know I'll never lose him since we're family.
A few months into our situation I started dating someone. It never affected our relationship though. Well not until a few months ago when my boyfriend found some explicit text messages I had sent to my cousin and forgotten to delete. I told him about everything and he cried, but never once threatened to tell everyone. We've since moved on and I haven't seen my cousin since although we're planning to see each other tonight. My boyfriend refuses to go to family things for that side of my family which is understandable. I also told my cousin that my boyfriend found out just so he'd know why I was being distant. He was shocked and upset at first but once he got over the initial shock we were fine. We still talk every now and then but its much more difficult now. My boyfriend has no proof that any of it is true so if we ever broke up he wouldn't be able to tell anyone. Nobody would ever believe him.
My cousin has given me the best sex of my life. He's 8 years older than me. He has the perfect size penis. It's big enough that its extremely pleasurable but on the brink of being too big. I don't think I could ever completely quit things with him.
TL;DR: I've been having sex with my cousin for the past 3 years and my boyfriend found out. I still don't feel guilty about it.