First- understand that everyone goes through this, everybody has an answer for you, but the answer that worked for them may not work for you. There's no right or wrong answer. A lot of people say 'the way to get over someone is to get under someone' personally I've never subscribed to that sort of thinking. It leads to unhealthy rebound relationships IMHO.

The only thing that will really fix this is time. So there is no magic bullet. There are things you can do to help though or pass the time faster. The biggest one is find ways to not ruminate. Focus your attention on other things, ideally useful things. Take some time to improve yourself in fun ways. Hit the gym is an obvious one, but I generally recommend take up a hobby or learn an instrument or take a class. Basically learn some fun new skill and focus your attention on that. It serves as a distraction from your grief, but also a source of engagement and a little happiness.
It WILL get better.