Honest question from a straight guy

So, growing up and living in a very conservative part of the country and in a religious household, there are some things about gay male relationships that I simply do not know about. Please know that I ask this question out of pure, honest curiosity, not judgment or stereotypes, etc. So, here's the question: In gay male long term relationships, are there true tops and bottoms? In other words, are there guys in the relationship that serve only as a top or a bottom? Thanks in advance for satisfying my curiosity. If this belongs on a better subreddit, please let me know. Cheers!