You'd want to find more info about what he's saying before you become too anxious thinking that something had happened.
If his work involves working w/ chemicals, it could be true. If you know of the other performers where the performance was to take place, you may casually check in w/ them.
You can look for other things such as how are the two of you are getting along in general, if the passion is still there, etc. Then, if there are any changes, determine if these are as a result of his stress level increasing, having some other difficulties ex: financial, dealing w/ his patent, etc.
His behavior does not seem to be suspicious in regard to taking his clothes off like that. If he wanted to be secretive don't you think he could of done it differently?
For now, you would want to make sure that you're not projecting this mistrust onto him unless there are facts to go by. Body language (where his eyes shift) is not always reliable. Are you suspecting that he's talking to his ex or a new person?
You'd want to get some sort of confirmation from others i.e. the guy who wanted the guitar in order to match your suspicions w/ the facts. He may feel wary sensing your lack of trust and acting this way as a result of it (protecting himself).
You welcome Judy.
Try to remember that men like to be more independent. He may want to fix things on his own first before he burdens you w/ his issues. That can reflect in his behavior. It would even be more stressful to him having to justify what's happening if you think he's being dishonest/unfaithful.
At least now you took it in the open how you felt and he had responded to you well.