Sometimes saying good-bye really stinks, but if it is good for the work, then you have to do it! Bite the bullet.
Here's the thing, you're the writer, you're in control. he exists on the pages you produce out of your own head. you could write another book with this character as the lead if you wanted to. Maybe what you are hung up about is that you want to describe him more fully, explore this character more deeply so you feel that the good-bye is premature because there is SO much more to know. Maybe you think that he won't get to grow and develop in your head anymore if you are not continually writing about him...no more little romps creating this guy...so if that's true, here's my advice (take it for the .02 it is worth), its your keyboard, just becuase he has to leave this book doesn't mean he has to leave all books forever, right?
Might just be the way your head is telling you that there is something else to explore with this character and maybe he is "too big" for this one book. He has more of a story to tell and he wants you to tell it (I know, I sound schizo when I say things about the characters in my head, that I made up wanting to you to tell "his" story - hopefully you know what I mean.)
Keep moving with it...his time will come!
Say "farewell, until next time, go save your race, and don't forget to pack clean underwear and a sandwich and see ya in the next book big boy!"
Trish