My Friend's Fiancee!!!

So today my friend's fiancee messaged me on Facebook. We were all very good friends at one point, and I love both of them and their little baby. They call him my nephew.

The conversation starts off normally, everything is fine. Then he starts asking me if I want to see pictures of her boobs.

Now he knows that I have a little bit of an attraction towards other women. He also knows that I am married, and that L (his fiancee) would NEVER go for it. She would be pretty upset if she found out about this.

He is now trying to talk dirty to me. I am doing what I cam to curve him. This is not cool and it makes me uncomfortable. Now I feel like I can't even go visit them because I'll know he's looking at me with lust.

How would you handle this situation?