<human>: Can you summarize the given text in a few sentences?

So I dated this girl about 3 years ago until she left me for another guy. Admittedly I had a lot to do with it because I didn't give her as much attention as she wanted. 

After our break up we stayed good friends and chatted once in a while. She told me about him and how he's mean to her and puts a lot of restrictions on her.

Recently she got fed with him and decided to break up with him for good (they "broke up" multiple times prior to this). So after breaking up with him she tells me she wants to get back together and I say why not.

Ever since we gotten back together, she tells me how she is sad about her ex. I'm no expert in relationships but I feel constantly mentioning your ex is not a good thing.

She tells me how how he messages her and tries to make her feel bad even though I told her to stop talking to him and block him.

I'm not sure how to feel or what to tell her. I've been taking this cautiously because it feels like she is using me as a substitute.
<bot>: Girlfriend who I got back together with repeatedly mentions how she is sad about her ex. Said ex is the guy she left me for in the first place.