I think if you spend enough time with him, his motives will become apparent. That's why taking it slowly before hopping into bed, as you are doing, is a wise move if it's a partner you are looking for and not quick sex. Go you!
Of course, there's no way to know for certain what he wants until he shows his hand, but there are some things you can watch for. A guy who is truly into you and looking for a relationship acts differently than a guy who just wants quick sex.
Behavior is key. Words are easy to fake; actions are not.
Relationship Guy enjoys spending time with you no matter what you're doing; he doesn't have an agenda other than just being around you. It's not always "Let's go back to my place" or "Let's go to this party and get shit-faced" (so we can "accidentally" end up in the sack). He is just as happy to hang out and study or go for a walk or run errands, as long as he's with you.
Relationship Guy takes you out on dates--not only that, but he is creative about it and comes up with things that are fun and different and unusual. He tries hard because he wants to impress you. He gives a crap, and it shows.
He also does things for you that he wouldn't do for just anyone. He hates talking on the phone? Not with you. He doesn't eat sushi? He'll go if you want to go. He's more flexible than Sex Guy because he wants to please you; Sex Guy is all about getting what he wants.
Relationship Guy wants to get to know you: he asks questions about you and your life: your family, where you grew up, what food you like, your career plans, what movies you like to watch over and over again, how you got that scar on your shoulder and who gave you your first kiss. He listens when you talk and remembers what you tell him.
He also wants you to know him. He shares things about himself--I don't mean prattling on about all his wonderful accomplishments and how great he is, but real things about his life. Who he is. What's important to him. His goals, fears and regrets. Real stuff, not BS.
Relationship Guy is drawn to you for the right reasons: your brain, your wit, your heart, your passion, your values. Compliments on physical attributes are nice, but if that's all you get from him, be wary. You are more than just the sum of your parts.
My usual caveat: none of these are hard and fast, and a guy can do some of these and still be a cad. You need to look for trends, and trends take time. That's why not rushing into bed remains, above all else, the best way to be sure what a guy really wants.
(btw.. thanks for joining us for the group chat last week. Your name jumped out at me as I was going through my question queue.)