One ex is my best friend. I know thats a line that can be stereotyped, but he was always important to me, it was just unfortunate (and very much not planned) for us to lose the romantic connection. I wouldn't give up his friendship for ANYTHING--not until he himself decides its time.
My boyfriend trusts me, just as I trust him with his ex. We are both adults and understand the consequences of taking those past relationships too far. I am very lucky that he understands how important my best is to me, and can sympathize with me when it hurts to remember what didn't happen.
As for the other exes... I play phone tag with one because I don't mind talking to her, although its pretty obvious she isn't interested in me without a romantic flame. Drama llama, as it were. The others are banished to the 'do not answer' profile on my phone--no ringing, no texts, no names. Just Over.