TIFU By sleeping with my friend

I understand that this kind of story is kinda dulled for this Page but a i wanna start anyway, and algo English isn't my star line up so bear with me. I (M25) have been working in a pizza buffet for almost 8 years, is was my first job and has been dulled down to the point I only go on weekends for half of the day, it's easy money and the hours are adjusted for my real job and school, in this time I've gotten to know the owners and their families, which includes their niece lets call her Sonya (F18) but a the time I met her she was 15 or 16, and at some point she started working with me at the buffet, so we worked together for over a year, and in that time I became a aware that she liked me, and maybe out off cowardice I never told her straight that I didn't want to be with her, her age being the deal breaker for me, as time passed she left the restaurant and went out had a few boyfriends and i remained alone. cut to September of last year where she started texting me again after 6 months of her turning 18 and not talking to me, cuz of her bf, she told me all about it and we had discussions and chats and how they ended things.

Now cut to last month when she returned to the pizza shop for weekend work, this is the part where I introduce my friend Mike (M20) who has been working with me for more than 6 months, he truly is my brother and my friend we've drink together, we've shared together, an absolutely unite of a homie and a better man than me. so Sonya liked him and told me if I could help I did outta love for my friends and convinced him to go out with us, she made her move and they kissed, I left with a forced smile and return to my house feeling alone and stupid, guess it was that I never got the chance with her. for the next week she told me all about him and how she is beginning to have feelings for him but he isn't looking for anything serious, i was glad for them but still felt like shh. and last week in talks with Sonya she told me that she used to have feelings for me and I said I knew, from that point it escalated and the next day we had sex. and now I'm in this awful point where I have feelings for this girl and she had or has feelings for me and my friend. we had sex couple times before we all saw each other in the restaurant and it was torture, she flirt with me and him and i just felt angry at me and her, but the people at work know about em and I felt impotent. and today they are still going out causualy and I'm still in a position where idk if I'm waiting o just doing things wrong, I am enamored by this girl, she has been in my live for some time and have more than a crush and I don't want to rush or ended, so yeah today I ef up

what should I do for the sake of my friend and my feelings for her? TL;DR i helped setting up 2 good friends and had sex with one a week later