I also wouldn't bother telling him, but it really depends how you feel. When he gets back, don't tell him for a month or so. If you feel it's eating you up, and there's a voice in your head going 'I need to tell him', then tell him. But don't tell him because of some preconceived moral that 'All relationships should be completely honest'. If you don't want to tell him, then don't. If you think you do, then do. It depends on your level of guilt.
And in the meantime, work on not getting so drunk that you kiss old sports coachers!