I am new here, but this post caught my attention. I am 29, single, and will be banded in Sept. While I haven't had a problem telling my friends and family what I will be doing, I can understand not wanting to make it a part of first date conversation.
That being said, I also think that before you let someone in your bed you should be able to openly discuss anything with them. If you don't feel 100% comfortable, just tell him you had laprascopic surgery. I wouldn't use the gallbladder, because that is an outright lie.
Oh, and the GYN nurse deep inside me also reminds you to use protection. Get tested, use a condom, and always be honest with your partner