I don't feel bad that my ex-housemate is basically homeless
Why are you so unsympathetic to her plight?
I don't care.  She's a bitch.
Did she do something to you? Being homeless is a pretty bad thing to wish on someone.
It's fine, I can't care about every single person I've ever met.
That's true, you can't care the same about everyone, but that doesn't mean you have to carry animosity inside towards people.