He dumped her 8 months ago because he didn't love her anymore. They dated for 2 years; she was crushed. I have been dating him for the past 3 months. She texts, facebook messages, and calls him often. His sisters and friends believe she still loves him, but he is not sure. He has stayed friends with all his ex's, which I don't mind, with the exception of this one. Because she likely still has feelings for him, and because he is now dating me, I feel it is inappropriate for her to behave in this way. What do you think? I don't care if they talk, just as long as she doesn't be secretive about it.

Whereas you may be perfectly reasonable and mature about low level contact, when it oversteps the boundaries it makes you anxious and possibly jealous, completely understandable. Talk to him about it, tell him how it makes you feel and why, you never know he may just be able to see it from your point of view and get her to take a step back to where she belongs; in the past.