Is oral sex considered cheating?

If ur married/in a relationship and some chick gave u a blow job, is it considered "cheating"? Could u in good conscience get a $20 blowjob from a hooker and still tell your girlfriend you've been faithful?

Conversely, if some guy ate out your gf but didn't really fuck her, would u consider that she didn't really "cheat"?

Or what if ur gf blew some guy...is dat cheating?