Do you think that Ennis defend his homosexual act in that way? - I'm top, so only Jack is queer. 
I don't think Ennis ever really THOUGHT about what he did with Jack. He said he wasn't queer and never gave it another thought. I think he was so twisted up with fear and guilt that he couldn't really understand (until after Jack died) what he really felt.
Psychotherapist M. Scott Peck, tells the story about one of his patients in his book "The Road Less Travelled." The parents of a young married woman (she was in her mid-20s) engage Dr. Peck to help their daughter. Her husband had brought her to live with her parents because he did not know what was going on and he could not help her. She had been a pretty and outgoing young woman, but now she spent every waking hour PRAYING. She barely ate, wouldn't bathe or clean herself, wouldn't change out of her pajamas and WOULD NOT go outside.
Dr. Peck worked with the woman for a few months. The woman had been married about two years to a husband selected by her parents. She had a strong religious upbringing. She had dated only the men her parents approved of and was a virgin when she married.
After a couple of years of marriage the woman realized that she didn't really like/love/care for her husband and she CONSIDERED leaving him. She saw a man she had dated briefly and CONSIDERED what it might be like to be married to him instead of her husband. She never actually talked to the other man, she didn't date him, only CONSIDERED divorce or an extramarital affair.
Her GUILT from just CONSIDERING other possibilities caused her so much distress that all she could do was PRAY.
Sometimes the difference between what WE WANT and what WE THINK WE SHOULD WANT is so painful that it can paralyze us.
Ennis wasn't stupid, but he didn't have much education. Also, he didn't have ANYONE he could talk to about his feelings. Alma? NO. His brother or sister? NO. A clergyman? NO. A therapist? So he stayed paralyzed and in pain.