1. He dates/flirts with other women in front of you
If he doesn't care that you're right there and he plays the "I don't care, and maybe she will get jealous" game, then he will treat you like that even if you manage to make him your man. No guy/girl should ever make their bf/gf feel like they are second best to anyone else.
2. He is always on his phone, even when he is in your presence
If you are talking to him, or you're out on a date and he is paying attention more to his phone than you, then he really doesn't care what you have to say. Spending quality time is about having your physical and mental presence.
3. He doesn't ask about you/your life
If you guys meet up and all he talks about is himself, or even worse all he wants to do is initiate sex, and he never cares to ask how you are or how your day has been- then he really could care less. It's true guys act how they feel.