I think if you feel he's trustworthy then you can trust him. See, It isn't really a question of the circumstances of his job but rather a more general question regarding your ability to believe your boyfriend.
Lets say he was working around a bunch of 20 year olds, you think he wouldn't be faithful if he loved you and cared about you? It's all about whether you have trust in your relationship. If you do have trust you must believe him, otherwise life together becomes impossible.