What should i do when my best friend and my boyfriend want me?

I'll try make this as short as possible. Ive been best friends with this girl for years now. weve had so much fun over the years doing everything together. she was my friend when I started dating who I'm with now I absolutely love him. but I love my best friend too of course! she got pregnant and had a child, I was her baby sitter for him since she worked. I'm her son's god mother I love him to death. her family is like my second family! so about a year ago, I went to some fair with my best friend, we ended up getting kinda close spending the day together alone.. we held hands and got close she would laugh and be all over me and yeah it is normal but there was a different vibe that day and her and I both felt it. so ever since that day I couldn't get her out of my head but we are both "straight" always talked about dick/dudes whatevs, i never mentioned my feelings. her and I have another friend who we are both close to, I told her my feelings, she told my bestie and my bestie told her she felt the same and couldnt believe it. months passed and I finally figured out she liked me although we both hinted we did, but I have had this boyfriend for like 2 years I live with him it's great! time passes, bf and I consider a 3some, I confide in my bestie and she says she wants to and I did to, so we all 3 had our fun. time passes and my best friend has not stopped talking about wanting me. she flirts all the time when were alone she touches me she kisses me. my boyfriend told me after the 3 some we could have sex together without him but we made a new deal that it's not okay. because I wouldn't want him fucking her without me so we decided it's a couples thing for us only. I have to literally avoid being around my best friend because she will try me an I want to of course she's so beautiful and the problem is I care for her too much to be doing that with her I'd catch feelings more than I already have! I don't want to cheat on my bf. my best friend knows how I feel and won't stop teasing me and it's hard. I don't know what to do. I didn't realize this was going to happen. she and her baby daddy still get together sometime and have sex but she wants me on the side because they aren't together at the time. yet she gets jealous or upset when I talk about sex with my bf now.. or anybody.. please send advice my way 😭 they're both so important to me! I love them both. I want them both in my life. at one point my bf and I even agreed to take her and her son in for a 3 way relationship! UGH