How to stay happy?

im 16 years old and im like a "hippie" person and i act and like that kind of stuff. im typically a very happy and positive person but the last week ive been sad and letting the little stuff get to me. Quite honestly, one of my biggest fears is to be sad, like i hate being sad SO much. recently ive been trying to not let the little things get to me and focusing on the postive, but ive noticed its been hard.
I feel like part of the reason is because a about a week i broke up with my boyfriend and wanted to stay friends, (which he is one of my best friends, so its not like weird) im not upset about the breakup at all, but i just found out hes moving and i love and care about him so much and im so sad hes moving. It just seem like when something happens to me and i get sad, everything hits at once and i let the little things get to me and it truly sucks. Considering being sad is one of my fears, Why is this happening to me? How do i maintain happiness and positivity? How to love myself completely?
Thank you for your time and reading this far, you rock my socks man!!!!(-: