How can you start flirting with your ex-boyfriend again?

We still like each other a lot but there were just too many things going on and we decided to end it despite how badly we really didn't want to. We promised before we started dating that we'd always be friends and we promised after we broke up we'd still be friends. But the thing is I can't talk to him without it hurting and I think he feels the same way about me too. When I see him in person, we just can't go back to the way we used to flirt and talk before we dated... we're no longer comfortable around each other even though we still like each other a lot. How can I talk and flirt with him playfully again like we used to before? I want to give this another chance... but I don't know how to start over again.How can you start flirting with your ex-boyfriend again?
Sounds like a complicated situation must've been something serious for you guys to break-up like that. But if you're both still in love with each other i don't quite understand why you two decided to break up in the first place. Regardless, sometimes relationships can make a friendship awkward but try to give it some more time, it may seem hard now but as time goes on it will get easier. I think you both need to talk about your current relationship and figure out things from there. Or if that's too uncomfortable just try to casually flirt with him and joke around like you used to and see how he responds. You could probably tell from his reactions what the best thing to do is. It might be hard but sometimes staying friends really is the best thing! Good luck and hope i helped!