It could be a lot of different reasons. He probably misses you, he's thinking of you, wondering how you're doing, trying to reestablish contact. It doesn't mean he wants you back though, he could just want to keep you on a string as a backup. Maybe he's just horny and hopes you'd do a booty call. Most likely he's just lonely and is looking to you for an ego stroke. Don't read too much into it, if he wanted you back he should be working for it. Don't let him take you for granted, don't be the easy girl. He will respect you more if you are a challenge, make him work for your attention.