That entirely depends on where in America you are going to. In the coastal metropolitans, people have come around and you will find vibrant gay communities, even whole city quarters, and being gay will be a fact about yourself like the food you like or the music you listen to.
The heartland is a different story, people in rural agricultural states tend to be very religious and “traditional”. Generalizations of course never work well, but there is indeed a distinct difference between the liberal coastal cities and the rural “flyover states”.
LGBT in itself is too broad a topic to recommend any specific online forum. I’m not gay, but from what I hear from my gay friends going on some gay forums that do not correspond to your particular personal orientation can get you flamed even more than outing yourself on some backwater “conservative” forum.
My advise, google your <destination city> + gay
America really isn’t one country. The mindset and attitude of people say from the Southeast and the Northwest couldn’t be any more different. So it really depends on where you are going.
We’ve got everything, from places where you can just be yourself without ever getting any grief for it to places where you will be overtly ostracized for your orientation.