Aw omg I hope everything is ok
Everybody gets over breakups differently so it may be hard to give you good advice.
But I would say, the main thing to do when you're feeling sad about it is to remember all the bad things in the relationship. Make a list if you have to. From big things to small things, anything that bothered you about this person or the relationship in general, to remind you that you don't have to deal with any of that anymore.
Distract yourself, go out with friends, use the internet, buy something that makes you happy. Limit yourself on time spent thinking about what once was, and focus on the now and the future <3