I'm going to break up with my fiance during his deployment
Why would you wait until he's deployed to break up with him?
I feel bad for breaking my word and doing so while he's away serving his country, but I don't want to be around him when I tell him.
I don't think it's right to wait until he's deployed to tell him. If you want to break up you should do it now, in person, before he leaves on his deployment. This way he can process the breakup before leaving.
I don't care. I want to break up.
Then you should break up with him before he leaves, so he isn't devastated while trying to serve his country. It's stressful enough to be in the military, and putting a break up on top of it could be really hurt him emotionally.