Sounds like she is having some difficulty finding the balance in her life now. The trials of being a single mom!
I think you're doing it right, approach the visitation changes w/business like attitude, don't just let her change her mind every week. Your s needs more stability than that. She may be struggling to find that happiness/balance to her life right now and more nightclubbing isn't going to get it.
Don't worry about getting bit by the jealousy bug. It'll pass. I'm still chuckling over her reaction tho. It was like, 'Since when did you get a life, Gabriel?'