It doesn't matter who you are, people leave. It's always for a reason, though. They leave because you both didn't need one another in your lives' chapters at that point in time.
Change is Good
No matter what happens, things change. If there is anything stable in a person's life, it is change. Good will always come out of it, maybe not directly, but it will always be good.
Life is What You Make of It
You could be given the worst situation that is impossible. You can't change it or fix it. However, what you can fix is your attitude towards the situation. The worst things can be the best ones.
Everything in Life is a Decision.
Even making a decision is a decision. You must use your decisions to help you grow and become a better person.