I apologize in advance if this is long. Names are changed
I have a 17 year old daughter (Amber) who has a guy best friend (18). We'll call him Brad. My daughter is interested in girls, has never shown any interest in boys, and has only dated other females. They have been best friends for going on 5 years now. Again, there is no interest from either side. They are in several classes together at school.
Brad has a girlfriend, Terri (18). They have been dating on/off for maybe a year. Terri doesn't go to the same school as them. Terri hates my kid. Terri knows my kid is a lesbian. When they all hang out, Amber says she is so mean to her, glares at her, or just straight up ignores her. If Brad says anything to Terri about it, she will hit him. Yes, she has smacked him in front of my child.
They have broken up a few times, but Terri pulls the "I'm going to off myself if you don't take me back" card.
Yesterday, Amber came home from school and was super upset. I asked her what was wrong, and she told me Terri hit Brad so hard in the head he has a knot on his head. Per his words, when he told her to stop, she began biting herself and scratching her face.
I've met this girl one time, and I automatically didn't feel great about her. Brad doesn't have a stable mom, so I kinda "adopted" him. He came over to our house to pick up Amber to go thrifting. I hadn't seen him in a few weeks, so I gave him a big mom hug. Terri got out of the car and told me to "get off of him." This is my first interaction with her. He told her to go back to the car and apologized to me. He looked so broken and beat down. When Amber got home that evening, she told me Terri intentionally scratched Brad's new vinyl record with a pen because he asked if they could listen to his record. They had been listening to Terri's vinyls for 2 hours.
Brad's dad is an ok guy, but he's not around a lot. He works a ton to support both his boys. Terri acts like a saint in front of his dad. I don't even know if he would believe me if I told him everything that's going on. From my limited knowledge, he's never told his dad anything. He told Amber he's scared to say anything because of the stigma. "Boys can't be abused by girls."
Brad is a sweet kid. Polite, works hard, and is a caring person. I'm scared Terri is going to really hurt him one day. I'm never one on one with him. If he comes to our house, Amber is there, of course.
I feel crazy getting involved in a teenage relationship that isn't even my kid's, but I'm really scared for him. He's like one of my own. I don't know if I would be overstepping if I said something to him or his dad.
Is there anything I can do?
TLDR: My daughter's male best friend is being abused by his girlfriend. What do I do?