My girlfriend makes my life so miserable, she doubts me so much for no reason, Help.....

I am in a relationship with a girl from the last two years. since I am in relationship I have got so many opportunities to mingle with other girls but I didn't availed thinking that I will disturb my relationship. God knows how sincere and committed I have been with her but she has been continuously doubting me and still she doubt me.. What should I do, I literally want to kick her ass and say good bye but do not have the nerve to do that...help..
My girlfriend makes my life so miserable, she doubts me so much for no reason, Help.....
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