So is it possible to have a truly platonic relationship with an ex-lover? How far can it go before it intrudes on her new relationship? Should she break her need for the guy or should her new lover just accept his continued presence in their lives?

When you say, "how far can it go," do you mean in terms of how affectionate they are towards each other or how much time they spend together?

Anything's possible. On a more serious note, it could happen if both parties acknowledge that it's over and they are just friends. Dunno what that chick's new boyfriend would think though, if I was him I would be wary and beware of the ex.

Well, SHE seems to think/know its over with her ex. But they still exchange gifts, and talk on the phone all the time. She says he is having a hard time with it though. Not to mention her poor new boyfriend (me). But how much affection should there be? Dinners? dates? what?

Hey if shit is gonna happen it's gonna happen. If you don't trust your girl with her ex then tell her ex to fuck off. I would do that if I were you. Dinners and dates? Unless you really trust your girl then I reckon those are no-no's.

If you tell her ex to fuck off (more or less), then you'd essentially be forcing her to choose between the two of you- and from the sounds of it, there's a good chance you'd lose, especially if you were the one to bring it up.

It's a tricky situation without knowing all the details. All I can say is, if you're not comfortable with the way things are between her and her ex, tell her that. You can trust her and still not like that it's happening. Maybe you could suggest the idea that the two of you shouldn't consider yourselves boyfriend and girlfriend yet.. if nothing else, it's sure to show you where you and her ex lie on her list of priorities.