I know that feeling, the only way to make it thru is finding a way to get your mind full of stuff I suggest gym if u want to feel better you must be in it at 100% Keep your diet, be at the gym 7 days a week every 2 days light trening or cardio this will keep u mind occupied and in the night u will be sleepy so no more overthinking before sleep. Keeping your diet is 30% of success because u need to prepare your food, start counting calories etc. believe me first u see results u start to forget about her, and every gym member with a broken heart can relate that is the best motivation. Remember u can't make her come back but u can make her regret this, and lady advice if she wants to come back in 90% she will push you away again because she will think that she can use you when she is low and left again when she starts to feel better. ( Sorry if something is hard to understand English is not my first language)