AITAH for sleeping with an old classmate’s mom?

A couple of weeks ago I matched with this stunning older lady in hinge and I messaged her and we talked for hours and decided to meet up and fuck, And so we met up a couple of days later at a restaurant and talked for a bit and it turned out she was the mother of one of my old classmates, and then we went back to my place and had fun, we did multiple times afterwards and we both knew and agreed that it was just about sex between us but I guess he found out somehow because a couple of days ago he messaged me calling me an asshole and a piece of shit for sleeping with his mom, keep in mind I haven’t spoken or even seen this guy in over 8-9 since we graduated.

But still am I an asshole?