I slept with my ex's friend

My ex and I recently broke up and I found out that the day I went into the hospital for medical issues that he was at another girl's house. The day I got out he was going out on a date with her. I found out from his friend and he (his friend) came over to talk to me and see if I was okay. I've always had a crush on him ever since I met him when my ex introduced us. He stayed for dinner and we slept together. I hung out with him and a couple of his friends also. We both admitted to having feelings for each other and he has been very affectionate the last couple of days. We both said we want a relationship, but then he says he's not wanting to date. We were just with each other and he is acting like the same affectionate guy he was a few nights ago. My ex doesn't care and we both feel bad, but should we?

P.S. I did NOT sleep with him to get back at my ex. I actually like him. ://