Why does he go for unattractive girls with little substance?

He's a Virgo sun/Leo moon/Libra venus/Cancer mars/Cancer rising.

I've known him for close to a year now and we dated casually in the past, but he never gets too serious with me… I'm not saying I'm the most beautiful girl in the world with the perfect personality, but if you were to see the girls he chooses to date long-term, you would understand. They're ugly ghetto girls who curse and can't seem to hold any type of meaningful conversation, but they're nice to him. A few even have kids. If he matched up to them, I would've moved on long ago, but he's NOTHING like them. He acts that way WITH them and then acts totally different with me. He's polite and intelligent and super sweet kinda shy and we have the deepest conversations. He says he wants to get married and that he really likes me (but won't say love yet), yet he still keeps me at arm's length and spends a lot of his time with those girls instead. For all I know he could be talking the same to them. But anyone could see I'm the most practical choice! What is going on inside his head? I'm so confused!

There's only one girl he's dated in the past who even remotely lives up to my expectations and he said he was young and stupid and messed up with her. That's all he'll say.