How often do regular stars collide/merge? Does this happen more or less frequently than with black holes? And is there a general reason black holes collide?

How often do regular stars collide/merge? Does this happen more or less frequently than with black holes? And is there a general reason black holes collide? Certainly they'll merge if they get too close to each other, but why are they get close in the first place? And since stellar mass black holes are relatively small, why don't they just orbit each other indefinitely (i.e. how long until we expect Jupiter to crash into the sun)? At what distance does the gravitational radiation start shedding enough energy that the rapid inward spiral occurs?