You like the stuff you do with him better than you actually like him. If he’s great at planning fun dates (always a positive quality!), you could be having a really fun time with him without noticing if you’re having a really great time just because you’re with him. No one is saying you have to stop having adventures, but if you wouldn’t look forward to at least the occasional night just hanging out with him on the couch doing nothing, he’s not your guy.
You forget about him. Sitting by the phone waiting for a guy to call or text gets old fast, so it can be a great thing to be with a guy you feel sure about. On the other hand, if you not only don’t wait for him to get in contact but you regularly forget to return his messages for hours or days after he sends them, he’s probably not on your mind enough to matter.