Bitch Pudding

Last summer my friends introduced me to a friend of theirs who I’ll call K. Within less than 15 minutes he had already asked me if I was single and wanted to hang out. I happened to be talking to someone at the time so I turned him down politely. A month or two later after things with the other guy didn’t work out I agreed to go on a date with K. We became close friends quickly and were also intimate, however neither of us felt ready for a relationship and were happy with the way things were. The friends that introduced us were not. They gave us an ultimatum: either stop hanging out and having sex or get in a relationship or we won’t be your friend anymore. Long story short we decided to try and date but neither of us were happy or ready for it. We broke up after about a month after our friends gave us another ultimatum of break up or we won’t be your friends. These “friends” manipulated the situation for what reason I’m not sure, boredom, jealousy, maybe something else. So K and I decided that we didn’t want these people in our lives. We stopped talking to them, blocked them on social media and on our phones after being harassed by them repeatedly. I ended up moving in with K as a roommate and we did have sex as well but it was just a friends with benefits kind of thing. As time went by I found myself falling for him. After about 8 months I told him I wanted to be in a relationship hoping he would get the hint. He said the same thing, but that he was interested in talking to an ex of his. I tried to be a good tried and encourage him to do what makes him happy. They started talking and after about a month I told him that I had feelings for him. He said he had feelings for me too, but he was in love with this girl and wanted to be with her. I respected his wishes. Now they are getting together and she’s moving in with us. I want to be happy for my best friend, I want to be supportive, I want him to be happy. But my heart hurts knowing it’s not me. What do I do? How do I continue to live with him and her? We have shared a bed for the last 10 months, we even slept in the same bed last night. He wants me to keep that a secret from her and he told me that if she ever asks me if he and I have had sex to lie and say no. He says if I tell her the truth and ruin his relationship he’ll never forgive me. But I feel so conflicted. He’s been talking to this girl for months, while sleeping in the same bed every night with me and having sex with me. What do I do?