So if you're doing this, make sure you let him know that you understand if he doesn't want to be friends. Then the guy will, point-blank, ask me if I'm seeing other people. Who you're dating? It's the "reason why" part of the process that gets a little tricky. This, IMHO, is something that should be clarified before anything starts.
Now, which of these responses is the problem, again?
12 Nice Ways To Break Up With The Guy You're Kinda Dating
Some people view dating as a social activity, having someone to go to the movies or to dinner with, no big whoop. At the level of commitment you are describing, an expectation of exclusivity is unreasonable. A lot of it has to do with the goals. I've been the guy-victim of this sort of thing once. Just for the record, hmsbeagle, as a young-ish urban guy, I think drjimmy11's comment above is completely out in left field.