Dont know How to behave around him?

He jokes with everyone. he ignores me when he’s around others. He makes sexual jokes or comments towards me when he's alone with me. F. e: he wanted to see me change clothes (underwear) not that long Ago. I thought it was a joke but he was serious. He waited. I didn't to undress before his eyes.
When we talk Its super awkward and uncomfortable between us. Like, we have no topics. When i joke he doesn't laugh and when I try to talk to him (small talk isn't my strong suit) he just answers. We only have a lot of long eye contact when we talk. But Thats all. Normally he is a very sociable guy. Sometimes I feel like he wants to get rid of me but other times he comes to me and makes these sexual jokes. We do have a lot of eye contact when we talk to eachother. I dont answer these. Im not in love with him and he is taken so I want to respect that.
He also talks to another girl a lot. They goof around, tease eachother and their having fun with eachother all the time. She’s gay and has a child. He knows this. I see him weekly (not on a date) and I have no idea How to act around him. He says he can't read me and that he accepted everyone as They are. I wish he Just wanted to know me for me. Just like he does with that other girl. Normal and fun contact.
What can I do to have this too? And How do I have to act around him?
Dont know How to behave around him?
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