Is this true?

Partly. He didn't get married for political reasons. That idea of maintaining his fiction of "availability" was part of the calculation. It was also done to show his commitment to Germany, his "marriage" to the nation, sort of like how priests remain unmarried because they are committed to god. The nation was Hitler and Hitler was the nation.

Hitler was known to be a queer (gay?)

Yes

It was because Hitler felt himself destined to sort out Germany's high place in the world, and did not want the distraction of a domestic married life. That was how he put it to himself.

No, he just had not got much time for women, and there was a bit of thinking that he should be seen as availible to all women, he married her the day before they both killed themselves.

No

unlikely

I have heard this said. It probably isn't the sole reason, but for propaganda purposes, Hitler did like to portray himself as married to Germany. He liked seeming to be god-like or above normal human concerns (as many authoritarian leaders do).

The truth is that Hitler was really mentally disturbed by all the things he had witnessed in his life. He had some extremely questionable personal relationships...like the one with his niece that led to her suicide.

Hitler couldn't love a fence post, let alone a human being. Eva Braun even wrote a letter to friends saying Hitler was an unfeeling psychopath