i don’t know what to do

On thursday, My best friends boyfriend and I kissed, a few times, while we were intoxicated.

For context, two summers ago i met him and he was my first love and i think still is someone im in love with, after i had move temporarily out of the city we all lived in he started seeing her casually and ended things with me. Fast forward to this past october and they had officially started dating and had plans to move in together in the city i live him and he is from. He came to visit on thursday with her and we all when to a bar. Me and him ducked outside for fresh air and got talking and he kissed me. We were both shocked and went over to an alley to chat were he told me this girl isn’t the love of his life and he won’t end up marrying her. We kissed multiple times more and flirted and tried to wrap our heads around what was happening but ultimately didn’t come to a close and tried to find her and we did. We all went home and they went back to his apartment together but we lied to her and told her i was sick in the alley and that’s why we disappeared.

I don’t know weather to talk to him first and get a game plan because i think we need to tell her but i’m worried that i obviously have unresolved feelings for him and subconciously acting selfishly because i love him

please help