I wouldn't do anything that might complicate her relationship with her current man; you'll just look as if you've got an agenda (which of course you have). No harm in staying in touch, monitoring the situation as best you can, given the distances involved, and having a shoulder ready in case she needs something to cry on.
And no, I don't think exes have to stay exes forever; people change. If you know why you broke up in the first place and are confident you've fixed it, then it shouldn't be a fatal obstacle.