When 2 become 1

Last Friday night, a couple of us went out for a late night movie, Madagascar. I realised something while inviting my friends to come for the movie. I booked 18 tickets via the net for the movie because I was expecting more than 12 people so I just asked as many friends as I could. Anyway, 1 of the replies I received was "I doubt I can make it because my gf can't come." Well, not exactly in that way but the meaning remains with the people involved remaining anounymous. Let me explain that I have TOTALLY nothing against my friend for saying that. That isn't the first time I've received such a sms and I know I've probably used that line more than once or twice while I was attached too.

What I would like to ask is when do 2 individuals end up being 1? It's like saying "Oh, my right hand can't touch floor because my left hand is touching the ceiling" or even "I can't be in Penang while I'm in Selangor." The difference is we are 2 individually different people, so what does Person A not being able to come got to do with Person B not coming? Of course I do understand that being a couple, maybe your girlfriend wants to watch the movie hence you don't want to watch it with your friends in order to watch it with her in the near future. BUT that does not mean you can't it merely means you don't want to.

Again, I stress that I have nothing against people who say that sentence because like I said, it's a perfectly normal thing to say when you're attached. I've definitely used it before and I ain't shy to admit it, but I'm just questioning it's "truthfulness" or "suitability" in such situations. I'll probably use that sentence sub-conciously if/when I get attached again but I just don't think it's the most appropriate reason to give your friends. I definitely think that a better answer or response would be "Gf can't come and I'm hoping to catch the movie with her so I'll pass." I hope no offense has been taken because I really don't mean any. I'm just questioning it out of all truthfulness.