I have been here. Exactly as you describe. If a guy says he doesn't love you like a girlfriend, then he doesn't love you like a girlfriend. I've discovered (belatedly, unfortunately) that there are no mixed messages with guys. This is not me being bitter - I've spoken to friends in similar situations and it's always worked out the same. He has everything he wants here - sure, he has to be up front with you if he meets someone else, but heh, that doesn't matter, he told you that it wasn't a proper relationship, so there's no guilt there for him. And that's if he extends you the courtesy of telling you about another women - some guys - not saying he's one of them - would just do a disappearing act and then accuse you of being a bunny boiler if you wanted to know what had gone wrong.
If he was that bothered about you, he wouldn't have been with another girl at a party.
Cut off contact with this guy for a bit - at the moment he has it on a plate. Go figure out what you want and give him time to figure out whether he wants you - as a proper girlfriend or not at all. But don't believe that this will develop into something more without action on your part - it won't and you're going to get hurt.