Ex is his best friend

Okay so say your friend is friends with let’s call her Jill.

So Jill and my boyfriend dated years ago.

Also my boyfriend and I dated years ago.

Jill and my boyfriend dated after him and i dated.

Jill and my boyfriend are best friends and have been for years.

But today I found out Jill and my boyfriend have had sex multiple times.

Would you be okay with this?