You say you were raised Catholic, yet doubt evolution. The Catholic church (and indeed most Christians) accept evolution, so I have to wonder whether that is still your faith?
You misunderstand - whether willfully or through ignorance (your language suggests you're a creationist, which can mean's your understanding could be either or both) - the meaning of the word theory when used in reference to a scientific theory.
Although in a lay sense 'theory' may be analogous to 'an idea which we can't prove', in a scientific context, that describes a hypothesis. In scientific parlance 'theory' means "a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena" (Merium Webster).
Thus, when scientists say "evolution is a theory" they do not mean to suggest there is any doubt about whether it is true, any more than they mean to suggest there's any doubt about the attraction between bodies with mass when they talk about the theory of gravity.
Darwin did not suggest humans evolved from apes. Both humans and modern apes evolved from a common ancestor, something which is well established through multiple lines of evidence, not least of which is genetics.
I don't fear death, merely dying, but when I was younger, I did fnd it difficult to cope with the notion of my non-existance. I actually find my complete lack of importance in the universe rather comforting now. It gives you quite a good sense of perspective.