I am coming from a similar situation. Feelings, love, sex and the connection can be overwhelming. My question is, why do you stick around and give someone your energy when he’s still in love with his ex? I completely understand that this is your best friend, take a step back and analyze what you want out of this. If he’s your best friend and if at the end of the day that is above all what is more important to you, then maybe take a step back with the sex and just be his friend. If you move on, and he let’s go, was he ever yours in the first place? Trust me, all of this is so much and probably could only be understood through your eyes and his eyes. But at the end of the day you are a Woman who has feelings and knowing he still loves his ex, while having sex with you does not seem fair to you at all. Best of luck with everything.