Poor Ennis. With his background and upbringing he was never going to find it easy to go against the grain (of either what society or even his own mind told him). The dilemma he had was his poor heart was falling in love with Jack but everything else told him he could neither accept this or enjoy. Never a man to be impulsive nor anyone who stood out, he simply tried to do what he thought he should. After meeting Jack, he still married Alma, after Jack painted a future which would have tempted many, he told him life like that would be impossible. He was never going to be a man who brought about change.
He sees threat against him or his family and reacts with violence. He does not have the communication skills to deal with his anger in any way but to lash out, famously after Alma reveals she knows about him and Jack. The only time he let his heart be triumphant was the reunion. What a joy that scene is, to see him totally out of character and dominated by love and not fear. If only he could have reached deep into those reserves more often, particularly when Jake told him at their last meeting that he couldn't live without him.
His lasting emotion was regret for what should have been. All of this portrayed effortlessly by Heath Ledger - an absolute masterclass in acting which will probably never be bettered - and summed up beautifully in the final scenes with the shirts. Simply one of the most powerful examples of the power of love.
Certainly the most explicit demonstration that 'love is a force of nature.'