Bf (25M) won’t defend me (24F) from his dad’s inappropriate comments

potential trigger warning

I 24F have been with my bf (25M) for about 4 years. Since I had my baby, it’s been nonstop inappropriate, sexual comments from his dad. They come and visit us a few times a year to see their grandchild and In the past he’s said things like “ you look like you workout all night”, “ you look good for having a baby” and “ I wish my wife looked as good as you”, and “ I want you guys to get family pictures, but beach themed so I can see you in a bathing suit”, literally in front of EVERYONE and he sees no problem with what he says. It gets worse, but I’ll get to that. Anyways, I HAVE spoken up and been like “ that makes me feel uncomfortable please stop that” but yet he continues. When I talk to my bf about how his dad is making me feel it’s always things like “ it’s a compliment, just accept it. One day you won’t get them and you’ll miss it.” Which honestly breaks my heart because you’d think he’d be outraged by hearing this. I’ve gone as far as talking to his Mom about how I’m feeling which again, I get brushed as “ I’m sorry sweetheart, that’s just how he is.” BUT TODAY, a big line was crossed. I can’t remember what we were discussing, but I had disagreed with what his Dad had said and he said, without hesitation,”I should put you over my knee and spank you.” The room went silent. I was completely taken aback by this and I said “ don’t you ever say anything about my body in ANY way again. That is absolutely disgusting.” I told my bf about this and he rolled his eyes and all he said was,” it was a joke. I don’t understand why you can’t take a joke.” I was so upset, I asked him if he thought it was okay for him to do that and he said no but to just stop taking things so seriously because he won’t say anything because “hates arguing with his dad”. I know I’m not overreacting, cause I feel like this is sexual harassment of some sort because this happens EVERY TIME they come to visit and I’ve voiced how I’m feeling to everyone and I’m brushed off. I guess I’m just asking what to do about my bf not sticking up for me when this happens because it’s gotten to the point where I wear very baggy clothes, don’t do my hair or makeup and try to avoid his dad so I don’t have to go through this, yet it still happens and I feel so alone. I just want my bf to understand how I’m feeling and actually stick up for me instead of brushing me off leaving me to defend for myself….

Edit: I just want to add for everyone saying to just leave him that I have tried leaving in the past for other reasons, however my child is used as leverage against me whenever I do try, which severely complicates things.

Edit 2: parents who have left similar relationships, how’d you do it? Obviously I know the lawyer part and setting up a safe place to go, but it’s the GOING part that’s scaring me I guess…