Well it really depends on what you want Blondie. If you are only after friendship, then you need to make this clear to him. If you dislike receiving his lewd messages, then you must also tell him, otherwise, in a way, it's encouraging him.
If you are happy to have a casual relationship with him, then that's fine too, but you both need to be clear on where you stand. It does sound to me, like he's a Facebook chancer, of which there are many and maybe he does have some kind of bet with his friends, as to who can score the most.
Just be honest and ask him what he's after. Bare in mind, lots of men do lie to get what they want.