Sadness for eternity....?

A week after my birthday, the only thing I got was a broken heart. My girlfriend of almost 3 years dumped me. She said it was because I didnt trust her, because when she would go hang out till 2AM with friends or go do other things I would ask questions out of curiosity like how was it, who was there, simple questions. If I did not trust her then why did I believe her stories? I thought its natural to be curious of what the love of your life does, to be interested. I did get jealous sometimes though, which I thought wasnt as bad as others reaction to things she does would be. She would talk on the phone with male co workers for hours, would ask what they talk about and simply get an answer "work." This was not a big issue I let it go after awhile. One weekend me and her had plans to go to her family cookout with 2 of our good friends, but shortly before the cookout she dropped all plans to go hang with a guy thats like a brother and she only sees him as a brother, he is married with kids. I was upset and she said she wants to go alone cause I was upset and didnt trust her, typical things. 1 of our friends went with her cause she was bored and they was planning to swim. She did not get home till 3AM, so out of curiosity I asked what they did, etc. She was tired exhausted and pissy so I stopped asking her and asked her friend because she was wide awake in talkative mood, Learned he was divorced also.... He calls her first thing in morning to see if she going to go hang with him and she wanted to hang with him alot cause she hasnt seen him in years apparently. Theres alot to it but basically she dumped me cause she said I didnt trust her an I get jealous. I felt it was somehow all my fault so i told her I would stop being curious and I did trust her but she said I wouldnt change. I took my car back because I needed it as much as her and she said that was my last chance at saving our relationship. She used me asking her friend questions a "last chance" excuse also. We talked alittle after and she said she will give me a chance after other guys get a chance..... I was fine with that but made the comment I wouldnt be upset as long as she didnt do anything ual with them and she responded bitchy 'it would just be another guy so why would it matter?' (shes had 7 partners, and she was my first.) I was nice and let her keep alot of things, even our bed and I been living with my parents sleeping on a small couch with a sheet. We had joint bank account and I didnt have a job at this time cause disabilities, I would tell her when her checks would be direct deposited and one morning she called me after telling me to not talk to her asking if I stole her money, said no just took my $30 out and she said ok, we talked and it seemed to go decent she said she will call me in a week. Later that day her boss called me haring me basically saying I call her to much at work and i stole all her money. She called me and kept losing connection and i was helping her out giving her info on stuff. Sent her a text asking why did he do that and did she have any part she said no, so I said I will report him to his boss for doing that to me and she said if I do that she will report me for haring her and get a restraining order on me and to never call text or anything. I learn shortly after that this "brother" of hers actually moved in with her and they started dating a day after she dumped me but she denied it even after one of her good friends texted her old phone thinking she still had it asking what her new man is like, she said her friend is retarded and on drugs. This has torn me up so much even after all this, the signs that she was probably planning to cheat on me with him if she didnt that night already. A week before she dumped me we talked about getting married on her vacation time and etc, which we discussed many times before but never had the stability or income cause we lived with my parents for awhile, she was jobless and going through a divource when we got together and I had a good job. At that time she only had alot of bills and a box of clothes. Now she has a very good job her own place etc and im the one with nothing but a bag of clothes, bills, jobless and a car that breaks down often. I do not understand, after all we have been through, endured, and all our good times how could she got over me and moved on a day after dumping me yet its been nearly 2 months and I still am so depressed and destroyed. Crying alot and wishing things can go back to how they were and maybe if I didnt ask questions or get jealous she may have not dumped me. I feel it is all my fault but my mom tells me she used me and shes no good to me, my friend says shes a cause she planned to cheat with this "brother" guy. I would like her back cause I still am deeply in love with her, but I am constantly tore up by memories of me and her, and thought of her and him. Especially on our o