Thomas rubbed at his eye and figured he should probably come clean with at least part of it. Not enough to make Jamie feel terrible, but enough so his son didn't think this might be a behavioural change he was supposed to be looking out for.
In the end, he left out the part about gay conversion therapy entirely because it wasn't something Jamie needed to hear. "I asked him to leave me alone several times and he didn't. He basically inferred that you're gay because you were raised by a single parent who, according to him, failed you. I just exploded because you're perfect and no one has the right to say otherwise."