It's dangerous to make generalizations based on a very localized pattern. Certainly, perhaps heterosexuality is becoming far less popular in your region, but you cannot jump to the conclusion that it is a phenomenon common to all.

Even if you could find proof that homosexuality is gaining ground, it's not necessarily for the reasons that you might think. It could just be a simple matter of it becoming more acceptable in Western society, and thus people who are on the fence about their sexuality are less pressured to fall any one way. In fact, now that 'homosexuality is cool,' you could even argue that they're more likely to choose it even if they're slightly more attracted to the opposite sex.

The point is that you can't prove anything, or draw any useful conclusions - though it's harsh for me to say this, and not very helpful or easy for you to do, you should just move on. Find someone else, keep trying, and you'll win eventually.