What is this slang?

I don’t know if this is a normal term because I’ve never heard of it until he used it.. what is “I want to be in your stomach?” It’s like they think they’re dick is so big that it reaches your stomach?? Like tf did you ever take health class??? Where the hell did this come from? I’m also more of a spiritual person to me this makes sense.

I can never tell if I’m being used for sex or that guys are just so sexual all the time. I don’t know if he has feelings but he compliments me, I’ve met his friends and their girlfriends. We text, he’s never called. He’s always like: “I wish you were here right now. I wish we were snuggling” He is lonely I can tell. We’ve been friends for 2 years. After we first had sex he seems more interested but is that because we had sex and now he thinks it’s accessible all the time? I don’t drop everything for him but when we do hang out probably once a month when I feel mentally okay with life to see him he is very nice. He cuddles with me and he will rub my hand and my feet in front of his friends. His friends do make sex jokes but like I feel like all guys do that? It does make me feel a little uncomfortable I don’t want to be used for sex. Unfortunately we can’t go out with nothing being open. I’d like to do something fun with him. He is 4 years older than me. Still kind of immature but I’ve been told all guys are like that? He does text late at night. Our sex is really good so yeah he does get horny which I mean I get it, he’s a guy. Do I ask him what his intentions are? I just don’t want to be used but if we don’t have sex then I think there’s still a connection. He’s a total goof but he’s got to mature. His intentions seem good but yeah. Like he said I wish you were here right now is it weird I want to be in your stomach? I’m like hahaha how dare you have sexual urges! I’m joking. I have other views on that. I said I might be free next weekend so we can do something then. He said sounds good. Like he was being cute, then he gets horny, I jokingly shut it down but still kinda accept and he says sounds good. I wonder if he’s hurt by that. Like he’s just got to communicate more.