All changes in life require time. It can be very hard to get over the anger and trauma and upset of a breakup. Don't expect it to happen right away even if you both want to be friends. Give yourself some healing time first.
Going out with Ex
I went out with my Ex after 6 months,and she told me stories of "friends",that stayed over at her new place.Guy friends.And the dates they had.It just hurt me more.I found out(too late) that she's not breaking my heart any more I'm doing it myself by trying to stay friends.I knew all along that I wanted more than that,but even her telling me she didn't love me like that didn't stop me from trying.
It may never happen
sometimes you may not become friends again. he might learn to get over it except the fact he may fall in love with a differnt girl and you might be just a bug on the windshield of his life. dont let this get you down flirt with other guys and make sure he sees if hes going to hurt you dont let him see it your allowed to flirt but remember he can to I know this is very disapointment but remember there are other guys.
Give it time
I have been able to be great friends with some of my exs. We're even able to share some stories and experiences that happened after our break up. This didn't happen overnight, it took at least 1 yr before we could start talking like this and it was even rough once we reconnected. But if the desire to remain friends is there, then this is possible. Now my exs are the some of the best relationship advisers I have since they know exactly how I am.
Don't Compare Past to Now
All relationships change over time. You grow, you mature. Don't compare what you had before with what you had now. It's like comparing elementary school with high school. They're simply different things. Find joys in what you have now.