Ex wants to be friends and have sex?

We broke up almost 3 weeks ago and said he cant trust me because I talked to a guy (just a friend but he doesnt want me talking to any guys) and betrayed him and didnt think of his feelings. He said he doesnt think he could ever forgive or forget what I did and then said if I wanted to have sex with him he would be ok with it. I have apologized and asked for forgiveness and for us to get back together and take things slowly while we work on things together but he said his heart just isnt into anything right now because hes hurt. He's really stubborn and said its almost impossible to gain his trust back but that I can try and hes trying to forget and forgive me for betraying him...Still says he loves me, misses me but things change from one day to the next and i dont know what to do at this point. Any ideas on how I can convince him to work on this with me and not make me feel like im alone in this? Also, why can he say hes ok with having sex with me but then say he doesnt trust me?