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Hello and thank you for using JustAnswer. I am very sorry that your partner want to end the relationship, I can understand how hard this can be for you. What I noticed from your brief description is that you have tried to be more amendable to him to try to make this relationship work. The problem here is that he has to make an effort as well, as repairing a relationships takes both partners making equal effort. If you are the only one that is changing than the relationship will ultimately fail because he will not change and some of the problems you two had will continue.
Right now you have to grieve over the loss of relationship and it will be hard, but you will overcome this as it just takes time. Try to write a letter to him detailing all of your thoughts and feelings about this break-up, both negative and positive. But instead of mailing the letter, instead dispose of it as you wish. A good way to do this would be to burn the letter...this will be very cathartic for you as you are letting go of your thoughts and feelings both literally and figuratively.
In addition, you can try a thought stopping technique where you wear a rubber band 24/7 and every time you think about him you are directed to snap the rubber band. This will cause a mild pain allowing you to re-focus your thoughts elsewhere. In addition, the brain will start to associate mild pain with thoughts of him, so the mind will try to prevent you from thinking about him on a subconscious level.
Ultimately you want to surround yourself with friends and family, and to go out doing pleasurable activities to help distract you and to help you heal in the mean time. There is not going to be a quick fix in coping, as it will take time, but you will overcome this.
Remember though that you tried to make the relationship work by changing, but he was the one that refused to change and it was his choice to leave the relationship rather than work on it with you. You cannot be faulted for his cowardice as you stayed, so do not feel that you did anything wrong. I truly wish you all the best and I hope you can heal from this very soon.