Ok you have no idea of how much of me you sounded like about never knowing what to say, and being shy around people and them thinking your unfreindly. Thats a confidence issue and I still have it from time to time still but im slowly getting over it. You think you dont know what to say but you just have to open up a little. And just do it. Honestly, its as simple as that you just have to reply. Even mmhmm or a oh ok. Because your still engaging in a conversation and you'll become more comfortable.
But as far as your question like #3: What made the friend become an ex-friend? And I hate to be the one to say this but just because hes married doesnt mean hes not interested. Some guys use it as a cover. My dad did it for awhile there are plenty of guys that are just scared to come out or even want it to be true within themselves. But just think about is it worth going back to past times?
As far as noticing gays you really have to watch. Like think what do you do? Watch how they walk, what there looking at. Just be really attentive. Personally, I look at the speed of how some people walk and mostly I see that gay guys happen to walk faster then straight guys. Oh and also know that they'll be looking at you too, looking for other gays around the area.
I hope I could be of some help,
Prince`