Cheating in tech school

My husband is in tech school in the Air Force & is in a class of 10. 1 of which is a female. No issue at all. He had started doing everything with her, no matter what she was there. Class, All meals of the day, they would work out together, study l. I told him it was frusterating he was always with this girl. He was not even really calling me much anymore. He had been doing sketchy things like going to sit out side of his dorms (she lives in the same building) & yesterday was the breaking point, he was going to a birthday party with his class. He told me their car was packed so he rode by himself in the back of a lift. “There & back” I saw them on the snapchat map at the same location when he said he was by himself and WOULd not answer his phone.

Come to find out I wouldn’t talk to him till he told me the truth and he had been with her the whole time and they’d been drinking.

This is my husband. Please help. If there was nothing wrong he wouldn’t lie. I have never tripped on him about other women