When you're not a priority, he won't call often and will take a long time to respond to your SMS. All the while making the excuse that you're too busy. You'll be perpetually lonely. So you spend time thinking about how much you miss him, till you become bitter. Bitter people get even by hurting those they love most... especially if they have the opportunity to hurt someone new. The next step is easy: Just like him. If he's not calling or responding to your messages then he wasn't serious about starting over with you. He's still seeing other women as unimportant. Move on.