'AITA for cutting off my mom after I caught my boyfriend cheating on me with her?'

My boyfriend cheated on me with my mother and now my grandparents are mad at me for cutting her off.

ClaraZert writes:

My boyfriend (18) is now my (18F) ex, obviously. But we were together when he cheated on me with my mom (42). This hurts even more because she was the one who encouraged me to ask him out. He and I have been best friends since we were 13. When we were 16, she told me to stop being afraid and pursue him.

I found out about their affair last week when I came home much earlier than expected (the professor was sick and canceled the lecture). I caught them red-handed. Mom tried to apologize and said that she ‘just wanted to feel young again.’ I still blocked her anyway.

Now, my grandparents are telling me I’m going too far, and that because she put a roof over my head and food in my mouth, I shouldn’t cut her off entirely. They think I should go home and eventually forgive her.

I am staying with my dad and will be asking my ex how long he has been intimate with her, to see if she has groomed him.

OP responded to a comment admist the judgements:

UseSuitable6549 says:

I’d try to get a straight answer out of your ex and find out WHEN it started. It’s weird to me she’s known him SO long and still saw him as a sexual exploit. I’m 30 and the idea of sleeping with an 18 year old boy makes my skin CRAWL. NTA (Not the A^%#ole). Stay away from that woman. She’s an adult. I wouldn’t even forgive her as my friend, let alone my mother.

OP responded:

I’ll talk to him and find out how long it’s been going on.

firstWithMost says:

A roof over your head and food in your mouth is nullified by free use of your boyfriend without asking.

IndependentWestern84 says:

NTA (Not the A^#&ole). Giving you food and putting a roof over your head is the bare minimum a parent is required to do by law so they don't get thrown in jail... your grandparents must be as fucked in the head as your mom is. Just live your best life with your dad and put her on blast, I would suggest you tell your ex's parents.

Zer0-Sanity says:

I'm so sorry. It’s really disturbing all around. So your mom basically watched him grow up? Did she know him before? Yikes. I would be furious at my mother, and probably never forgive her.

That’s some betrayal you just don’t do to anybody, let alone your own daughter. Mothers are supposed to pick up the broken pieces of a broken heart, not help cause them.

What do you think? Is OP right to cut off her mother?