Staying friends with an ex is a nice theory but I do wonder how it plays out in real life. Jealousy can be a thing. I know that I've seen that with my own GF who is visibly bothered any time that on of the others I've dated / been involved with cross her radar.
I've almost always stayed friends with my exes - (except my ex-husband, no thank you). It hasn't been an issue except for my current boyfriend - CMM has a HUGE jealous streak. Like, my high school boyfriend turned Catholic priest who said the services for my mom - CMM had a huge problem with that. Really, if he didn't have terminal cancer, it probably would be a dealbreaker for me.
I don't flirt, most of these men don't have designs on me (certainly not the Catholic priest!) - we just maintained a friendship after we parted, usually very casual (like my college boyfriend who I see for lunch about once every 5 years). I think if you are confident in yourself and your partner's behavior doesn't give you any reason to be suspicious it shouldn't be an issue.
