Here’s the deal: He either wants you or he doesn’t. There’s no grey area. If he tells you he “isn’t sure” about being with you and he “needs time to think about it” then, to cite the great epiphany of the mid-00’s, he’s just not that into you.
You’re not a dessert; you’re a person. He already knows if he wants something serious with you or not; there’s no reason to sit around and let him string you along. You really, really are better than that.
Let that guy go. He’s not the one who will stand by you through life’s inevitable difficulties anyway.
Find someone who wants to hold your hand no matter what. You’ll find the guy who considers you a priority when you get rid of the guys who view you as just an option.