Well, to me it sounds like he's exploring his sexual tastes, trying a different flavors at the ice cream store if you will, with the breakup as his primary motivation. There's really not much guys won't tell you if you hang out with them often enough and believe me, I used to work at an auto shop and was always a tomboy, so I've hung out with the guys alot and heard alot I shouldn't have had with the promise not to tell the rest of my "species" but this is not really a new one. It may be a good thing but just remind him to be careful out there. We really don't want IT falling off......
EDIT: Oops, sorry, forgot to add this part. If you were with this guy and plan to still be, let him know of your concern. He shouldn't make you uncomfortable if he still wants to have the benefits plan with you. He needs to know because this will affect your relationship with him.