Ex-girlfriend is playing games?-need everyone's advice!!?

My ex-girlfriend who broke up with me back in November has frequently called me over the past few months telling me that she is miserable and misses me. Oh yeah, she broke up with me in an attempt to rekindle the flame with her separated husband who has treated her terribly over the past few years. She has also told me a few times, "I think we both know it's not over between us" and "You don't understand how much I've thought of you the past two months." I care about this person, and that's why I keep answering her calls. Why is she doing this, I don't understand!!! Please give me some advice on this situation explaining her behavior!