Why do I keep ending up with unstable girls?

It could be the places you hang out. If you hang out in computer rooms and libraries then yea you might find a weirdO. Sorry but most normal people are out having fun at a bar, or sports games, shopping at the mall. So don't meet anyone online, or at a coffee shop, or at a math or computer tournament. Its just the way it is. A lot of those types don't have real life experience except at the computer. Now in the long run this can bring you lots of money. But most of the time the people that work on computers is men. So just keep looking and maybe you need to change your preferences on women. Maybe you are subconsciously choosing these types and not know it.