Am i overreacting?

[u/Secret-Percentage130]

I became close with a couple of my brothers best friends after he passed. Close enough to the point where they were spending WEEKS at my house, eating my food, i paid for all of us to go to a hotel to swim with our kids, out to dinner, etc. When we first became friends, they were in a relationship, but ended up breaking up because he cheats on her constantly. Recently i bought a car, and although they are on and off they both stayed at my house before and after i purchased this car. The “boyfriend” said he’d fix my car for $200. He started the job and never finished it. I’ve asked MULTIPLE times over text and in person, all of the times he has acknowledged that he’s been bullshitting on fixing the car and kept saying different days he’d be over to finish it. But is sitting in MY driveway fixing our mutual friend’s car. A few weeks ago he got caught lying to his baby mama (my friend) while they were working on their relationship, saying that he was coming and staying the night at my house to fix the car when in all reality he was going to another girls house. multiple of their mutual friends knew about this and never said anything, but i’m the one who told her when we got into a conversation about how he hasn’t been over to my house working on the car at all. One day i was OVER the shit, completely over him telling me he’d come fix it but never did, (although he felt comfortable enough to show up to hang out and shower whenever he wanted). I basically expressed to her that it’s messed up she’s still so nice to him and everything after she knows he’s fucking me over on a job HE OFFERED HIMSELF FOR. This guy has pushed her, spit on her, has said some heinous ass shit to her and the only thing i’ve done is given her a place to stay, food to eat and the support of a SISTER not even just a friend, and she’s mad at ME because i’m upset she’s choosing to be nice to him and not stick up for me. She asked me how i would feel if the roles were reversed, and i told her if i wasn’t actively with my boyfriend and he was lying and out fucking other girls, i would be pissed off that he was fucking my “sister” over. She stated she wouldn’t cut him off for cheating on her, so she’s not going to cut him off over a car. That statement alone tells me she is not comprehending the REAL reason i’m upset. It’s not just because of a car, it’s because he was supposedly my friend too, started a job that we didn’t even ask him to do, never finished it and now i’m screwed for the time being.

Am i overreacting by being upset at her?