It was bound to blow up in our faces eventually. I mean i cared about that a lot less than my stepdad (who realistically to me is dad), but I had somewhat less to lose than him. We had been having s** since shortly after I became legal age over a year ago, and I doubt it ever would have happened if I had not been the one to make the first move and then pushed for it to keep happening. And his initial guilt was terrible for him because not only was he cheating on mom but with her son, and he had never done anything with a guy before. But I was there for him sincerely and not because I wanted taboo or s** or to take some sort of revenge against my mother for the s***** way she has treated me and my sister for years but esp after she married my stepfather. But when we became lovers it was because of how we felt/were close as well as comforting and consoling to us both. I get that it was double the hurt for mom, because if it had been my sister it would have been bad enough and mom was even more freaked out because she said she had no idea I was gay. Amidst all the blow up when mom my sister came home unexpectedly from shopping they walked in on dad f****** me and it was passionate and vocal befor3 we realized they were there. As soon as mom came off with omg my son is gay even my sister shouted “really mom how could you not have known?”. And my sister did not do herself any favors by making it clear she had known about us for months and her bottom line was that at least he and i had found something special with each other. That set it all off again. So by the time the shouting died down yes of course mom felt betrayed by everyone. She stormed out and dad and me and my sister talked for a while to make sure she was also ok because we were impacting her also. Dad needed to leave for a while to just clear his head and my sister and I talked for a while. I wanted to know she was ok despite that i was responsible for blowing up her world as well and she swore it was fine and she did not blame me for being close to him and because he is so subtly incredibly s***. She even teased that she was jealous that I had gotten him before she was ready to make a move on him and we laughed. I told her that if she wanted to then sincerely go for it because I was not the jealous type and i was all for her having some happiness in her life as well. Dad got home a few minutes later and it was awkwardly silent and then dad was relieved because my sister and I could not take it anymore and just busted out laughing, and he shook his head at us and told us we were insane but that was why he had always loved us as his own. My sister teased back about clearly some of us more than others and he did not stop himself before he blurted out that it was not his fault that it was because she was still underage and he did not do j*******. My sister got wide eyed and shot me a look that I understood, and i just smiled because i felt that the three of us would be together and ok and my sister knew that I would be ok if that day came for her and him.