I am so pre-filling my reply card too. I don't blame you either. It's your wedding and your paying for it (or someone is) and it's about who you want. I just had this conversation with my father about my 1/2 brother who is 15 years younger than me and lives in California and whom I've talked to for all of 5 minutes in my entire life. I told my father I'm not inviting him and he was like, well it is blood, and I was like this is true, but he's still not invited with how expensive each plate is and I don't even really know him. Same convo with a guy friend like yours, and I told him no he can't bring some chick I don't even know...plus why would he bring sand to the beach...hahaha
So you go gurl and stick to your guns!