Kissed my best friend

Okay ladies, I have come to a little problem. My ex girlfriend is my best friend. We were talking about why we never kissed or did anything else in our relationship. She said she couldn’t take not knowing anymore, pulled me close and kissed me. So in the back of a school bus we have this whole make out session. That whole story is fine besides the fact she has a boyfriend.😰

(Looking for advice)