AITAH for refusing to kick my little brother (17m) out of my place at my girlfriend’s request so she (21f) would feel better about moving in with me (22m)?

I (22m) have been taking care of my little brother (17m) for just over two years since our dad died (our mom died a few years before that). Both had very bad health. He lives with me and goes to the local hs by my apartment. He had to switch high schools to the one close to where I stay bc my parents were in a different area and he works whenever he is not in school (he works TWO part time jobs during the school year and works full time throughout the summer) bc even though I took him in he has a lot of expenses (I just can’t afford to cover it all) and wants to save up for the coming years. He shouldn’t be in this boat at all but that’s life. He is so young. Life has been very unfair to him and he is a really good kid. I have been dating my gf for just over a year. She wants to move in and not contribute to the household expenses bc I shouldn’t charge her rent bc she is not a tenant and I am not a landlord but we are boyfriend and girlfriend and I should be happy my girlfriend wants to move in with me (and I guess not contribute anything to the household expenses bc she sees it as me charging her rent). She also wants me to tell my brother to leave so we can have the space to ourselves and she can have more space. She has referred to him as a “freeloader” even though he is just a kid and I got myself to become his legal guardian. I told her no way. I think I should break up with her over just suggesting this but I don’t know if I should go that far and maybe should try and get her to see where I am coming from.