No.
He isn't cheating. Now, I reccomend thinking deeply on what else in you or his life could be making him distant. Has something at work been putting him under a lot of stress? Have you been rather demanding lately? Maybe he's having family troubles and doesn't want to stress you out over it. If he seems bored with the relationship, there has to be a reason for it. The main threat to any relationship is always stagnation. If you've both been too busy, figure out how you can see each other more often. If you're spending too much time together, find some outside interests and give each other space to breathe. If you want to have a more in-depth talk about this, you can always send me a private message.