Am I over reacting? (relationship help)?

[Ada]

My current girlfriend dated this ass hole for about 12 months up until she dumped him around the start of November 2013. He would text her dozens of times a day, message her on Twitter and Facebook throughout the day, send her Snapchats, call her, etc. He is a complete ass hole; she has told me some of the things he'd do while they were dating like hang out with girls she didn't want him to, he would get mad at her and yell at her almost on a daily basis, and when she would be crying he would just ignore her and play video games or watch TV. Anyways, this harassment lasted almost two months before she blocked his number and all of his social media.

I would talk to her and try to help her with her relationship problems with him. Then I found out she liked me, so we started "talking". He found out and would threaten to slash my tires and beat me up. He is crazy. Before we were official, one night she text me and told me that she had been texting him, which really effing pissed me off. I was very close to just telling her "you know what. Take him back, I don't even care anymore." but I didn't. She knew it made me upset, so she stopped talking to him completely and that's when she blocked his number and social media.

Just tonight my girlfriend texts me that she wants to apologize to him and make things "okay" with him; not be friends, just be "cool" with him, and I'm in the worst effing mood. Am I over reacting for thinking she'll get back with him/still likes him?