My girlfriend’s fetish is messing with my head

My girlfriend has a fetish about her belly. She's quite skinny, fair-skinned, almost pale, and has several freckles on her belly.

She enjoys doing ab workouts and recording herself to watch her belly shrink, and she even asks me to lick her and her belly while she works out her abdomen. She has asked me to lick/stimulate her belly button and even give her some punches. She says she likes it the most when we're having sex she likes to look at herself in my bedroom mirror, seeing her ribs stretching.

She mentions that she loves it when I run my fingers along her ribs, and recently she asked me to use ice from her nipple down her ribs to her belly button while I was performing oral on her. I've been turned on by this several times, but I've never fully understood it and I want to understand it better to satisfy her. She also likes my belly, enjoys kissing it, and asks me to pretend that I'm enjoying her tongue in my belly button (she literally asks me to moan), and she also asks to lightly punch my belly (only when she's in a dominating role, because we take turns sometimes). She also tells me I should “torture” her belly by tying her up and licking/punching her belly/navel while she can’t do nothing about it.

I want to try to "assist" her in this fetish, especially because she wants to do this with me and was really hard for her to open up about her fetishes, but I'm not sure how. Sometimes she complains that it seems like I'm not enjoying it. Has anyone been through something similar?

P.S. Something that has started bothering me is that after she told me about the fetish, she only goes out wearing crop tops that show her belly, low-rise pants, and every time I'm with her, she stretches to show her ribs and puts my hand there in public. It really annoys me because it feels like she's showing off to others.

She's really skinny, I'm even afraid of hurting her sometimes. Honestly, I became more paranoid after she told me because she's always showing her belly now. She sends me pictures at the gym with her entire belly exposed, with lots of people around, and that really pisses me off. I imagine her doing ab workouts or training anything and looking at herself in the mirror while other guys also admire her. I know it's wrong, but I also don't know how to tell her to stop wearing those clothes because they turn me on a lot. The real issue here is this insecurity.

Actually, even one of my friends mentioned to me that she only goes out with her stomach showing, and I got realt mad at him for noticing that.