If it creeps you out, then that is important in itself. You need to set your own boundaries on what you're willing to accept.

At the same time, fantasy isnt always tied to reality, though this situation seems to have quite a bit of crossover. Many guys will store situations from reality into their mental catalog for later fantasy (ie "spank bank"). Theres a chance he might not be interested in meeting up with her, she'll leave his class or graduate and he'll never speak to her again. He might entertain a fantasy for a few hot minutes, but draw the line professionally in reality. Whether there is anything intrinsically wrong with the scenario is of less consequence than whether you feel respected by it. Spouses need to determine their sexual boundaries as it best suits both parties, and that requires some vulnerable communication. Realize that you accidentally tapped into a deeply personal aspect of his life. If it disgusts you and there is no resolving it, then walk away. If you are okay with him having wild fantasies, you can help fulfill them or not and you can also ask him to respect the boundaries of your comfort (for instance: cam girls might be in, active students and sending money might be out).

I guess what I'm suggesting is to communicate with your spouse. If his attitude towards this is a dealbreaker, then walk. If you're able to approach in a supportive way, and he's able to express a set of reasonable boundaries for his fantasies and maybe even reel them back so you feel more respected, you might be able to tap into a deeply fulfilling sexuality with your spouse. Maybe something along the lines of "I don't want you getting that from students/camgirls/strippers how can I make you feel that way?"

While your feelings are valid, your approach to the situation can be either constructive or destructive.