I don't know what to do

I've always lived with my parents. My mom has major depression and well, I was a daddy's girl. Not in a rich spoiled way, far from it. I've moved out before but my relationships didn't work and they always told me to come home. Well my dad found out he has cancer 3 years ago. My mom couldn't take care of him fully due to depression. I did everything for them. EVERYTHING. no help from my 3 older brothers. He passed away 2 years ago. my now fiance continued to stay and take care of my mom. She got sent to a mental rehab. We took her, we visited every weekend. Then while there she broke her hip. She had surgery and I pretty much ed bathed her, cared for her, and took her to physical therapy 3 times a week. Then she had knee surgery. Now she needs a full knee replacement. I also had an ectopic pregnancy in the midst of all this. I'm so drained. I feel like I'm suffocating. She's in a better place now mentally and can care for herself physically. Well me and my fiance wanted to put a house on her land so I can check on her but we already have another house on the land my brother (who is a 30 year old child) lives in. This house is from the 1920s and is falling apart. She doesn't want to ask him to move so we can tear it down and put a house there. She said im not a mother and wouldnt understand. That hurt because she knows i have fertility issues and lost my pregnancy. My brother never comes and sees her or checks on her, we want to be there to do that. He has to grow up. I said I can't stay with her forever, me and my fiance need to be alone bc it's healthier for our relationship but she keeps saying why I doing this to her and I'm hurting her. She thinks it's my fiance ' s idea to move now she says she's beginning to not like him. It wasn't his idea. We both want to be alone. I know she is scared but it's not healthy for us here. We're never alone, if we go somewhere she calls us or gets upset we went without her. I'm 27 years old mind you. She cares more about how my brothers feel, who have done nothing, than how I feel. She gave my brother 5000 dollars and I never ask for anything. Why doesn't she want to help me or see how I feel when I have done so much for her and my dad? How can I make her understand? I've told her everything I've felt but I'm at a loss.