My boyfriend just got his sugar glider about a week ago, and he's been licking his butt for about 2/3 days now, is this a serious health problem? Should we bring him to the vet?

And it just looks like it's moist down there and a little bit up his tail

If you are concerned, a trip to the vet is always a good idea.

It is always recommended that any new glider in your home have a well check up with a glider experienced Vet to make sure there are no health issues to be dealt with. Fecal testing is also recommended to make sure there are no parasite issues that require treatment.