Am I the jerk for making a joke about my brother's affair at his wedding?

When I was in elementary school, I was a type of kid who got Disrupts class often on

their report card so I never focused much on school.

My district had this system where there would pair high schoolers with younger kids to

help them with school, etc.

My mom made me do that after I kept getting in trouble, so my tuner was a freshman Abby.

She would come over to our house after school to help me with my homework or something I barely

remember.

My brother John was the same age as Abby so they would talk to each other and they ended

up dating.

She stopped tutoring me officially after like a month, but since she was at her house

a lot, I also talked to Abby a lot and we were close as well.

Fast 4, 10 years and Abby and John got married and had a kid together.

Five years later, John tells me he's getting a divorce because he's met someone new.

It sucked because I like John and Abby together a lot, but whatever.

Then he tells me he had an affair with his new girlfriend.

It's also sucks and I told him he shouldn't have heard Abby like that, but whatever.

I also asked Abby how she was doing and she wasn't doing well, but she told me she didn't

want her to be the reason I have a bad relationship with my brother.

However, two months before the wedding, Abby calls me and tells me that my brother's

girlfriend has been harassing her non-stop.

She showed me the text and his girlfriend was saying some pretty disturbing things about

...