In the novel, Tom self-identifies as "queer" on at least one occasion. The implication seems to be that his mannerisms have identified him as such to Clay.
Clay smiled patiently. “I’m straight, Tom. Straight guys know how to drive standards without instruction. It’s instinct with us.”
“Very funny.” Tom wasn’t really listening. He was looking after the departed odd couple, and that pulse in the side of his throat was going faster than ever. “End of the world, open season on the queers, why not, right?”
He also takes extreme offence to a woman accusing sodomites as having been responsible for the world's ills
The plump woman laughed softly, but tears were in her eyes. “Ward!
I’ve heard a lot of words for it, but never that one. As if I don’t
know what men like you want with a tender girl like this, especially
in times like these. ‘They repented not their fornications, nor their
sodomies, nor their’ “
“Shut up,” Tom said, “or I’ll hit you myself. And unlike my friend,
who was I think lucky enough not to grow up among the holy Hannahs and
thus does not recognize you for what you are, I won’t pull my punch.
Fair warning. One more word.”
Clay certainly makes a lot of assumptions about Tom's lifestyle after seeing his apartment
“Follow along down to the kitchen,” Tom said when they were in the
house proper. There was a pleasant smell of furniture polish and, Clay
thought, leather, a smell he associated with men living calm lives
that did not necessarily include women. “Second door on the right.
Stay close. The hallway’s wide, and there’s nothing on the floor, but
there are tables on both sides and it’s as black as your hat. As I
think you can see.”