Yeah, leaving has its downside, your wife and child would be alone much more often, and the hurt that she would feel from the breakup could worsen her behaviour.
Or it might not.
I think only you can figure out these scenarios to any degree of accuracy.
What should I do? Is not an answerable question for us.
Other than being honest to her about your feelings and fears I have no useful advice.
Hopefully someone who has gone through this scenario will post something more useful.