Is it normal to keep thinking about the end of a relationship before it starts?

Whenever I like a guy and think about asking him out, I just can't *not* think about what will happen after we break up. It doesn't prevent me from asking them out or anything, but I think about what will happen with my day-to-day life once we break up (the guys I like are usually ones I see often at places I have to be, such as school or work). It's not like every single guy I go out with is going to be "the one" and we'll be together forever, and I think about bumping into them often and how awkward it will get. Is this normal?