Hey Tallulah. How're you doing?
I've been to a few funerals for people who were just teenagers. It feels awful and I can understand you feelings of tearfulness and anger - it can bring about a real mixed set of emotions.
I think the fact that you're going to a thanksgiving service says a lot. Though the passing of this person is terribly sad, it's important to focus on the good, positive things that happened in his life.