Why do you have to tell him about the surgery? Are you going to talk about his athlete's foot and cronic snoring on the first date too?
Remember that it's taken hard work to lose to almost your halfway point.
The WLS isn't a Scarlet A on your chest.
I go out to eat with people that don't know all the time. Get something healthy for you that will look like you ate a lot. Salads are helpful with that because who wants to eat all the lettuce anyway. I've also gotten those slider hamburgers before and just taken the bun off.
The thing is, I've also just eaten what I want and if the person was stupid enough to say something to me, I just said I wasn't as hungry as I thought. Hell, you could just chalk it up to nerves.
You don't ever have to tell him, unless you all get married and go for life insurance. Then, you might want to mention it.
Just have fun. It's a first date.
VSG 10/18/11 If you don't like the road you're walking, start paving another one.-Dolly Parton