Missing little brother

Ha

So I have a little brother who I had a close relationship with.. He was the sweetest kid until he got a gf. She comes from a VERY rich family and even though we tried to open up to her and invite her to all family functions.. she was always uncomfortable being around us. We thought she was just a little shy but then her rich dad bought her a house and she got my brother to move in with her. My mom asked if she could have their new address so that she can at least send some care packages but my brother said no. We werent even allowed to ask where they were moving. He just came home one day, packed all his stuff and left. They got into an argument and they havent spoken in about two years. Just because he got into an argument with my mom, he cut off the rest of the family as well. Both of them are still VERY close to her family. They celebrate every holiday with her family and post photos of family vacations as well. My mom still pays for his phone bill but he wont answer or text us back. My mom also paid for his car.. but then he got into a car accident and he had the cops tell us that the car was totaled.. he left it at the junk yard for us to claim and never did anything about it afterwards. My mom had to go and handle everything after the car accident because he didnt want anything to do with us. During that time I had a baby. He never even contacted me even though I would send him photos and ask him out for lunch. Now my baby is turning one and it’s her first birthday. I sent him an invitation two days ago but no answer. My husband says we need to just leave him alone. He was also close to my little brother but he thinks that we should let him have his own space. I say two years is enough. My mom has apologized through email and text but still no answer. She cries everytime there is a birthday or holiday because she misses him. What else can I do? It’s killing me that I dont even know what I did for him to treat us like this. I understand his fight is with my mom and not the rest of the family. I just want answers! Also during that time, my older brother went through some tough times and tried to commit suicide. We had to have a family intervention and called him but he didnt answer back. My older brother and his family then decided to move out of state so he could get into a rehab. He called my little brother so many times but he didnt even bother to text back. Should we just give up? We miss him so much and we just want to know hes okay now.. but theres no answer. His gf makes slime. She has about 100k followers on Instagram and he basically follows her to ever convention and helps her set up. My son LOVES slime and wanted to go to the slime convention but I didnt know what would happen if we ran into them so I told him no...