Most dads would rather be told they have terminal cancer than have their son tell them he is gay, particularly if it is your only son. Coming out of the closet is a selfish act. It turns your problem into your family’s problem and forces everyone around you to live a lie. I have seen this destroy families. If you are gay, stay in the closet.
If the above is true, the father does not love his son unconditionally, or possibly even love his son at all. He only would love his son if he were straight. So he will lose his only son, with no real compassion for the son's life or troubles. He wants the son to lie to him, so the son will not seek connection with him at all.
"Son, if you do anything I wouldn't like, be gone with you."