I think a lot depends on your home country and how culturally as a whole they view gay people. Also, your faith/religion and what it teaches about homosexuality.
That being said...from what you describe it sounds like your husband may be really blaming himself for "his son being gay" if he was an absent father, not really there for his son while growing up and believes that environment makes someone gay.
I was raised in a pretty strict fundamental Christian background and had it drilled into me from a young age that gay people choose to be gay. Which I always found a bit strange because why would you chose to be attracted to the same sex...when to the core of my being I found men to be desirable, hot, sexy, etc.
Anyways one of the young men at my church and I were and still are very close friends (his parents thought that we would marry)...anyways, turns out he is gay. He came out to me when we were in college and thought I would reject him as all of our other friends from church had done...I was the last one he told. He told me about his struggles from the time he became aware of his sexuality...like 12 or 13 years old. And he struggled and prayed for years that God would take those desires away from him. Finally he just couldn't suppress them anymore...he had even been engaged to marry a young woman and probably would have if she hadn't broken it off.
I think he might have married a woman and had kids and the whole package for his parents that he also wanted to please...because they have never accepted the fact he is gay and refuse to believe that it is anything but a choice.
From what I have watched with him...his parents have never and probably will never accept that he is gay and he moved out of state and away from them.
You may never be able to change your husband's mind...or over time he may become more open about the idea...I fell a lot will end up being cultural...here in the US it is more acceptable to be openly gay. I don't know about your country...sounds like it is not the United States.
I am sending you a huge hug..because I know whatever path in life my children take I will always love them and want the best for them...I know you do too. If you believe in prayer, pray for your husband to come to a place of peace about the situation. God loves us all, gay and straight.
Oh and give your husband a bit of time to sort out his feelings before you bring it up...at least a few days...men take longer to sort through their feelings...