My F21 boyfriend M23 said someone awful in front of me and our son, AIO?

Just to make this quick, here are some things to know. I am a step mom to the 4 year old and his mom sadly passed away a few years ago.

Earlier today we were at my boyfriends parent house, our son went to go upstairs to play with his grandad and his auntie (boyfriends younger sister) but literally 5 minutes in he is brought back down to the living room because it seems like his grandad hates spending time with him, personally I think he’s a prick.

So since our son was brought downstairs not wanting to he started getting upset that his grandad wasn’t playing with him anymore. He was so upset he wasn’t allowed upstairs to see is grandad or auntie and was having a breakdown asking to be left alone and that he just wants to go upstairs.

Seeing him like this is really upsetting as no matter what me or my boyfriend try to offer or do he just doesn’t seem to calm down. My boyfriend was really frustrated as our son was crying and crying and had been for a while, I don’t know what caused him to say this tho. He said “I’m done with this shit man, the pussy wasn’t even that good.” I was honestly shocked, I know he didn’t have a good relationship with his ex but what the hell went into his mind to say that?

I’m sure our son didn’t hear thankfully, but I was so angry. After our son finally calmed down we all sat on the sofa and I was just quiet. My boyfriend kept asking what was wrong, which I’m honestly surprised he didn’t know why. I told him how I felt and that the comment was highly inappropriate to say especially in front of our son. That’s all I said, but deep down I was thinking that it just sounded like he regretted him. My dad would also say similar stuff to me and my siblings when he was angry at my mom.

I don’t know what to do, I’m still hurting but he’s said he’s sorry. I just don’t know what went through his mind to say such a thing..