My Mom’s Boyfriend Keeps Flirting With Me In front of Her

I’m at a loss. It’s so normalized that I don’t even know if this is weird anymore? I’m 21f for context.

My mom’s boyfriend has been in my life since I was about 13. He’s never lived with us, but he does come over frequently. He’s watched me grow till now, I’m now 21.
He’s always made weird comments here and there about me and my body. I’ve always known it’s weird, but my younger sister said he acts weird to her sometimes too and now it’s throwing up red flags. I’ve laughed along at these jokes even when uncomfortable because how do I stop a conversation mid in its tracks to confront him when my mom is cheering him on?

Some of the events I recall: When I was 17 or so, I made a joke to my mom about making an OnlyFans (not in great taste, I realize), he was in the room and said to let him “proof” the images before I post them. My mom laughed along.

More recently, I feel like it’s gotten a bit worse? I wore a dress not too long ago and I feel like the comments are becoming more vulgar. Maybe I’m only now realizing? After wearing that dress, he complimented me at least twenty times that day and now the three stories after that happened.

To paint the picture: He had some sort of pad on his belt, kept on by a magnet near his groin area. I didn’t know what the pad thing was, so I asked to see. He hands it to me, I analyze it, and I hand it back to him. My hand is held out and he says, “why don’t you just put it back” and slightly juts out his groin area. I told him absolutely not and just put the pad in his hand, that was the end of that. This is the only interaction I can think of that my mom wasn’t nearby for.

Recently, I was wearing a tank top and he made a comment about if I could step out of the light since he couldn’t stop staring at my tits. I asked if my mom if my shirt was really see through, and she said she didn’t even notice. He then said, “oh sorry for being weird! I wasn’t trying to be weird!” and as I was about to tell him it was in fact weird, my mom immediately spoke up and told him not to worry because it wasn’t weird. In his defense, he did find me to apologize privately after this one.

The very next day, my mom put him on speakerphone because he wanted to talk to me. He had bought me a gift (which has been common as of late), and he stated, “yeah, after seeing your tits the other day I’m just madly in love with you”. After brushing him off multiple times, he kept telling me to stop being hard to get or that I was just playing hard to get. One of the times he said this, he said it to my mom on the phone and had her relay the message to me. She heard every comment and laughs with him. I did accept the gift, so maybe I’m the problem?

Aside from these, it’s just little comments here and there. It’s always been that way. I’m more concerned now that my younger sister (15f) is telling me he is weird to her and actively invades her personal space. He will go into her room when he comes over and wake her up by getting close to her face and sniffing her. (??????) My sister says he always does it as a joke and over exaggerates the sniffs, so he isn’t prefacing it as being an outright creep. I still think it’s so weird. I don’t like the idea of any man going into my young sister’s room alone.

How do I approach this? Do I go to my mom or him? I feel like if I mention it, they’ll just ask “well why’d you laugh along then?” “Why didn’t you mention it sooner?” all the things I didn’t do. I don’t know how to even approach if my mom gives me a “why” question, I think it will crush my world. My only fear is this is the ONLY person my mom has. My mom has zero friends; Her boyfriend is her only interaction to the outside world, she’s been with him for years, and he’s nice to her. He buys her gifts and pays attention to her interests. At the same time, I need to look out for my younger siblings. This guilt is going to crush me and I don’t know what to do. I’ve spoken with my psychologist on how to even handle this and I still feel like I’m at a loss. Why can’t he just act like a normal 50y/o?!?!

Just to add: He has his own biological daughter he had as a teen. She’s very much an adult now, but I think it’s worth mentioning. I hope to god he doesn’t treat his own daughter this way, considering he’s mentioned feeling like a step-father to me and my siblings. I don’t have a Dad, my parents divorced right around when my mom and her boyfriend got together. My dad was verbally and physically abusive to my mom and my siblings, my mom’s boyfriend knows this. The boyfriend has been in my life for almost ten years now.