You can breathe AND play the guitar? That's cool!
No, seriously - I must say breath noise has never been an issue whilst self recording - squeaky chairs, dogs deciding to come into the studio to see what I'm up to, telephones etc., yes!
Assuming that the guitar is around waist height and you are using a fairly close mic facing the guitar on the axis of the strings somewhere between the sound hole and the neck then it shouldn't really be a problem. Are you using a directional mic? An omni-directional mic might pick up more than you want.
But you are probably going to have to concentrate on breathing silently as best you can if it's still a problem.
P.S. - you're not trying to BLOW it are you?