<human>: Can you succinctly summarize the text in 1-3 sentences?

I am in a relationship with this girl who keeps messaging her ex boyfriend. It was an abusive relationship. He cheated on her, forced her to stop talking to all her guy friends, and overall treated her like shit. He was always on her ass about her weight and made her super self conscious. They were off and on for about a year. During their time together, the girl I am with now got pregnant and got an abortion. He forced her to do it, saying she would ruin his life and that she would be a terrible mother. Because he completely destroyed any power she had in their relationship, she followed his request against all of her beliefs. She got really depressed as a result and debated killing herself. It took her three weeks to tell me, which is reasonable, but uses this reason to justify talking to the ex on a daily basis. She is not having a breakdown and needing some immediate help and comfort form him, which I would be fine with. She has been talking to him consistently everyday for 8 days as of today via snapchat. Her parents are also unaware that this happened to her. 

I am concerned because of the fact they have a huge history together and have broken up before for several weeks until her ex does something to get her back. Because of their history, it would be pretty easy to get back into things with him. I brought it up to her and expressed my concern and got into a huge argument with her over this. She thinks I am being unreasonable and childish for asking her to stop talking to him. I would also like her to confide and look for comfort through me but she does not want that as the end goal. I can not help but see myself as always being number 2, behind her ex.

What should I do?
I do not want to get hurt in the future which I can easily see as a possible outcome. I feel like my concerns are justified. Any help would be great. Thanks.
<bot>: girlfriend experienced a diffucult past with her abusive ex and continues to talk to him on a daily basis, not sure what to do