So some back ground. This took place in a very isolated work place. I am a 21(f) and last summer I had sex with this guy 38(m). I knew he had slept with my big sister 26(f) and that she might have had feelings for him but every time I confronted her she would say "I don't know" or "who cares I am independent". I would ask him if there was any feelings between them and he would say "there is always feelings in these thing you know?"
They were not a couple at the time, he was dating another woman and cheating on her with my sister. But I had a feeling she was in love with him. Neither of them would confirm or deny feelings or anything. I slept with him a lot. And I feel like I started getting feelings for him. But I stopped because it felt fucked up. After all the things we did, she told me that she loves him but he is dating someone else. Every time I would cry and tell him I want to tell my sister he would say she wouldn't understand and that it would only hurt her. It became a stupid cycle where I would come over, tell him I wanted to stop this and confess, I would cry, he would comfort me and we would have sex. (He didn't care about me. I am just an idiot for feeling more than I should have.) Fast forward a few months after quitting and getting space, he left his girlfriend and is now dating my sister seriously. I spoke to him about there relationship. I asked him if he would cheat on her like he did the other one. He said he has been good so far but he loves women. I feel like I am being crushed by this lie but he said it would break her heart and that she would be more angry with me than with him. Basically saying that she would never speak to me again but most likely forgive him. He is very charming. WIBTA for confessing months later to her? I just feel so bad. And so stupid. She deserves better than both of us but what's done is done. He thinks it would be unneeded pain for me and that it wouldn't change what they have so it's best to just keep my mouth shut. I've been thinking he is right but it's hard to be around both of them knowing what I've done and what he has done.