you're seeing someone casualy, we only see each other once a week maybe more, we don't talk alot if anything not everyday, we've been dating for 3 weeks, we have had sex twice and I stayed over.
but I haven't met his friends or gotten invited and he spends alots of time with them and I know some are girls. but when I ask about it he gets kinda freaked out like I'm checking up on him. so is it serious or still casual?

It's still casual

The moment stuff of yours ends up in his place or vice versa, like the odd CD, toothbrush, or anything, really -that's when it could be considered becoming serious. If you're not talking that much at all, it's not even "friends with benefits" at this stage.

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"... I don't simply wash my hair, I make love to my hair, it is a process and it shows..."

I assume you turned to KR because you don't want to scare him off by talking to him about it and intend to take example from other peoples' personal experiences? I'm sorry that I can't speak from experience so I don't have that to offer, but I really think that if real clarity is what you want then confrontation is the best policy. You should tell him that you don't want to freak him out but that you yourself are uncertain as to where you stand with him. Bring up the subject casually, when you're in bed with him or something. Maybe suggest that you'd like to hang out with his friends some time, get to know them better.

Going only by what you've written on here it sounds as though he doesnt think of it as serious at the moment. I mean the fact that he hasn't introduced you to his friends is a big clue. Men get scared off with the big "where are we going with this?" talk, well any i've met do anyway. So, maybe you could suggest a group night out? Maybe you and your friends and he with his? To ease him into the idea...act casually about it at first....then if that doesn't work have a proper talk.