I’m with PBA (as usual) – bring it up.
If you two are really close enough hashkafically, he (I’m assuming it’s he) is cognizant of the reasons you don’t like Facebook and won’t think you’re crazy for calling it a “no-no”, and you can have a normal conversation about it. If, on the other hand, he can’t for the life of him understand why you’re against it, you’re not on the same page hashkafically. Eventually, one of you should be willing to give in – if you’re not willing to make sacrifices for the other, it’s better you find that out now.
Hatzlacha!