Ennis was gay, he fighted against it all his life because his dad traumatized him when he was a boy (the dead Earl scene). A few hints... the reunion kiss scene, he initiated the kiss and what a kiss it was.

The first ''fishing trip'', the whole scene on the mountain, Jack caressing his ear and cheek at the end of the scene... Ennis doesn't push him back.
The flashback scene from their last encounter, once again he is the initiator tought this scene is maybe an intimate moment but nothing sexual, he was just happy to held his lover (and was obviously in love).
The two shirts scenes, the first one when he finds the shirts...

:\'( The last scene, still with the shirts... Jack I swear... :\'( :\'( :\'(
What was it? I swear I loved you, I swear I regret... I don't want to go off topic but IMO Ennis was gay, he was just the victim of his epoch, life experience and education. I know it's sad
