Hey man, if you wanna change your life around i would firstly try and see what it is that is exactly making you feeling like this, women, life success, fitness or mental health what ever it is find out and then attempt to build a new life with new experiences, hobbies etc. These things will make you have more fun in life and in the end make you forget about the girl you lost and how amazing your life is now!
So in general don't sit and ponder on how bad life is, get some new goals, activities, jobs and experience life your here once go get it man

your meet new women via doing this anyways so chin up tell me how it goes. hope this helps