Maybe just be honest with your mom and say that you aren't planning on leaving your husband (I assume) but that you worry, rationally or not (since she'll think it is irrational probably), and you need reassurance that help would be there if needed. Just be honest that you worry and that the worry makes things worse.

It's hard to have to have that kind of conversation. I have one friend who I have mastered it with so I usually try to pretend I'm talking to him (or do talk it through with him before trying my mom/therapist/sister/whomever).

Needing reassurance is ok even if others don't see the worry the same way you do.