How do you deal with nostalgia, sadness? Do you have nice methods to cheer yourself up?

Edit: I'm working on myself lately a lot. I am trying to improve, but I catch these sad emotions constantly (I'm one month after a break up) and honestly I don't know how to deal with it. They slowly eat me inside. Even if I'm having a big smile on my face and trying to give good positive vibes for my friends and family.