4. He leaves a toothbrush at your house or gives you his keys to his apartment.
It's an old trick, but one that speaks volumes about where a guy's head is at. If he insists on having a toothbrush at yours or makes room for your contact solution in his bathroom, he's planning on having you around for a while. The ante is upped when he hands you a set of his keys. It's his way of saying that his house, aka heart, is open to you.