Lez be honest

Recently my best friend revealed to me that she is a lesbian. I was a little shocked but still I supported her. Yesterday out of nowhere she basically confessed her love for me, to me. It was really awkward because I'm 100% straight and I also have a boyfriend that I am in love with. After talking to her about her confession, something crazy happened. Long story short, we ended up having sex and to make things worse, my boyfriend walked in on us. I'm really confused about what I should do. I need advice, help!!