I'm not going to let my mother move in with me and my boyfriend.
Is there any reason why you don't want her to move in?
She has almost ruined my relationship on several occasions and I'm tired of it.
If the situation is dire for her, lay out some ground rules if you allow her to move in. If it's not urgent, tell her she can't move in.
I don't want her to interfere in my relationship. It's personal and I don't want to share anything about it.
I understand, you don't have to discuss it. Just know there are options available to help ease the tension.