HiCustomer Thank you for asking your question on JustAnswer.
If you do not want to ask him straight out if he is seeing someone because he will only deny it then you only have two other choices:
1. Believe that he is telling you the truth that he is busy until you have concrete proof of his indiscretions and have trust in him that he isn't seeing someone and that the change in his behavior has nothing to do with cheating.
2. Do your own kind of detective work as far as his whereabouts and what he does when he is not with you, check his phone when he isn't around, emails, text messages, maybe talk to his friends if you can trust them not to tell him and see if he has said anything to them about seeing someone else, when he says he is going somewhere check to see if he truly goes to where he is saying he is going, see if he has changed how he dresses and his appearance, or if you can afford it hire a private investigator one with a reputable business that knows what they are doing and isn't just in it for the money.
Those are the only choices you have if you feel he will not be honest about whether or not he has been seeing someone else when you ask him. If he did not buy those things (one fairy magnet and one fairy crystal) for you that it isn't typically something a man buys for himself he could have bought them for his mother is she is still living or a sister if he has one that isn't really a tell all to his cheating.
Thank you again for trusting us with your problem.