TLDR: GF watches 4 yo brtoher more than mother and it is beginning to feel as a burden on our relationship and her own progress in life.

So I understand this title is a bit confusing but my gf has 2 brothers one is 18 other is 4 yo and she is 20. So our relationship is great and we talk about everything but I just can't find a common ground on this one. So obviously her mom had her other son later and I feel it's beginning to be a burden on the relationship between us. So he has just started pre K recently and her mom recently got a new job as she has been job hoping and everything's inconsistent. Because of this and with her being a single mother I feel as if my gf has taken a role as the 2nd parent even though she says it is not like this. I can not make plans in advance for dates, time together, or just free will from her as she lives with her mom still. We have spoken about moving in tg & the mom said she could not move out until February. I love her to death but working around someone's schedule as if we r in highschool is insane to me. I have been doing all I can to help her out career wise and all the bells and whistles. But at what point do I need to speak with her mother.

Because of the burden of taking care of her brother she restricts herself on where she could work and the hours available, when we can be tg, and just flat out freedom.

So now that we got the meat I'll explain it better. So I live on my own with my own transportation and all that. she is practically the opposite. I typically spend all weekends with her and that's where we get most of the time tg. But in the last 2 months more and more often she's either had to stay home and watch her baby brother or bring him with her. This is fine however this limits what you can do as being with a 4 yo is not fun sorry if u think so. With the job she has now never working around her requested hours my gf gets the brunt end of the stick and I do to. Not a big deal tho right? Well say a weekday I wanted to spend time with her. Well it can't be anytime because her mom has to know everything all the time and if not it's a lie just so we can be tg. I completely understand family comes first but when do I tell her mom to make the sacrifices for her kid instead of my gf. I just feel as if the situation is extremely unfair to our relationship and puts an unnecessary strain on us. I feel as if she is being treated as a kid still even tho she is 20 and will not stand up to her mom to appear as a bad child or bad sister. (Messed up family situation I won't share but let's just say it makes things a little more difficult (trauma))

AITA for wanting her mom to take more responsibility for her younger son and be the one making sacrifices instead of my GF who needs to start focusing on herself so we can make better progress towards our futures and family if we pursue that