My best friend was having problems at home so we invited her to move in with us after graduation. She got into it really bad with her mom a few weeks before, so we decided to move her in then. Everything was great until her boyfriend was always around and she is never home. We want to kick her out, but I don't want to lose her as a friend... what do I do?

Is she causing problems or not paying or doing her share?
If she is doing what she needs to then you should pick your battles and tolerate it IF possible.
You can evict her but you have to do it according to your state law.
It would be a written notice for her to vacate within xx# your states law days.
If she still does not leave then you go to court and file for another eviction notice. Then when that day comes if she still refuses to leave the constables will come and escort her out.