Dating multiple people to find the person to be in a relationship with, acceptable?

I really hit it off with this guy, it instantly felt like we've known each other forever and we just constantly texted for a week straight. Usually I talk to people, and sure we have lots in common, and they seem like my type, but there's never this instant chemistry, it's just 'polite' conversation. With him it felt deep and connecting somehow.

Anyway, we go on our date a week after talking, and it goes really well, grab some food, hang out and we're making out in the car, and I can tell he's really up for stuff and I'm trying to not go there cause I've never done it on a first date, but I'm really into it so I'm just like whatever, if we both like each other, what's the big deal? We're supposed to meet up the next day too since I'm leaving for a month to visit family. Shit happens, but it was great (and I don't regret it, I knew full well that it might not work out, but I liked him enough to not care). I'm really into him, you get the idea...

He's shown his interest in multiple ways, like going out of his way to show he's interested in me and letting me know he's glad I'm into him too and all the usual stuff.

When we first started chatting, he tried to be a little sexual - I guess to test the waters. One day when he wasn't up for going to work, I said he should stay in and he asked would I be his 'nurse' if he called in sick? I of course took that to mean, would I satisfy him sexually. I said 'as long as I'm the only nurse' cause I don't want to be one of many girls. so he says 'if we work out, I would never hurt you like that'. I should have asked for clarification or made myself more clear I guess, but that was good enough for me, I made it a point that I'm not into that. That if I said 'as long as I'm the only nurse', I meant 'as long as I'm the only person satisfying you sexually'.

Thing is he's still chatting up other girls to go out on a date. My friend messaged me one day (I had him added on Facebook, he likes all my posts and comments on most of them. I put up a new profile picture and my friend commented that I looked great, and he liked her comment without realizing who it was), and she says that she recognized him cause he messaged her on the site and wanted to go out and she asked if I knew him in real life, what he's like. etc. I said how we went out and were really hitting it off. That kinda bothered me.

I told my friend to see if he's up for more than just a date, and he's totally down for just hooking up with her. Am I in the wrong for feeling bothered? I mean, he said 'if we work out' which can mean anything, maybe he meant in a relationship sense. But what I don't get is, why try so hard to show someone you're interested, tell them you can't wait for them to get back so you can hang with them, and yet try and find other girls to go out with or get with? I saw his conversations with her, before she messaged me, and they were so plain, and not at all like what we had, so I know he's not into her like he is me for sure, but why bother if there's nothing there?

I'm trying to not let this get to me and hope that when I get back, this gets more serious so he doesn't have to look for other dates, but I feel like I wont be able to hold out and that this is a deal-breaker but I don't want to just bring it up.

What's going through a guys head when he's into a girl but is trying for other girls? Does he think he doesn't have a chance and is checking his options or what?

Sounds to me like you are just moving quicker emotionally than he is. He implies he'll not see anyone else if and when you become an exclusive item, which seems fairly normal to me. I'd hold on for a bit and see if things become more serious, then hold him to his promise at that point. If you can't handle that in the meantime then tell him what you want explicitly, no games or cryptic language, and accept that you may or may not have to move on as a result.