I blew into my boyfriends urethra will anything happen?

No, with low pressur: Blowing into the urethra at low pressure will cause no trouble . At high pressure one could cause air to enter the blood stream and create an air embolism which could cause shock and even death . We use KY Jelly in the urethra but again at very low pressure . There are reported cases of KY jelly embolism to the lungs. So my best advice is no blowing into the urethra. Blow Job is a misnomer.