I've seen similar descriptions of snakes that are just having a runny poo due to something they ate, such as if their owner fed them a chick instead of a rodent one feeding.

I've also seen similar descriptions of snakes that are expelling some sort of parasite such as a tape worm.

Assuming you have not done anything different with his diet, I would be very concerned and take him to the vet. Even if you did do something such as feeding a chick, I'd take him to the vet just to be sure. If you can collect some of the runny poo and bring it with you, that can help the vet diagnose the problem. Seal it in a ziploc bag and store it in the fridge until you go to the vet's office.

You'll need to have your boyfriend's female (or is it yours? ownership changed from one thread to the next) checked out as well, since they were together and the parasites could have been passed from one to the other.

How is the female anyway? Did you ever get a weight on her? Is she showing more signs of being gravid? Do you have your incubator ready to go?