I think Jack's biggest hang-ups were reality and Ennis. If Ennis had been willing to commit early on Jack probably would not have married.There would have been no reason for him too.It was not even as if he wanted kids.He unoubtedly had a higher sex drive than Ennis,hence the trips to Mexico,but I do not see that as a hang-up.
In view of the no commitment from Ennis he saw Lureens money as a way of esacaping at least one area of his life he was unhappy with,the grinding poverty he had come from.I do not mean that to seem as cold hearted and calculating as it sounds.I am pretty sure one gesture from Ennis and he woud have given it all up to live with him.I guess no Ennis and no money was too much to bear.
As far as his childhood goes ,I guess there would have been some hang-ups associated with his father,but not sufficient to stop him living the life of his dreams.He was forever the optimist,and as long as you have your dreams,that can make up for many a shortfall in reality.Take away the dreams and reality then bites hard.
Jack in the last meeting with Ennis surely feels the last remnants of his dream,get blown away on the wind.It is at this point that that his dreams maybe become his biggest hang-up.Hence his explosion,reality sucks.So could it be that Jacks dreams,once his greatest comfort,finally become his greatest hang-up, ultimately,the shattering of which,leads to his death.For Jack I do believe up untill then,hope had always sprung eternal.
He has I believe already died emotionally,when his dreams of a sweet life with Ennis died.All that remains is the physical death,which seems almost a forgone conclusion.Unbeknown to him,Ennis by trying to protect his lover has in fact done completely the reverse.Therein lies the horrrendous tragedy which haunts,Ennis and will continue to do so,and also us the viewer.Never has the phrase,we always hurt the one we love most,resonated more devastatingly.
It could be argued that whisky is a problem for Jack,but again had his dreams come to fruition,there may have been little need to drink so much.I am sure alcohol was a way to deaden the pain.In much the same way a his initial clowning around is in part a mask he uses to hide his true feelings for Ennis.
Reality therefore is ultimately the biggest hang-up for Jack.He is unable to deal with it.He hides behind,alcohol,sex trips to Mexico,marriage,clown masks,and dreams.But behind all those maskes is the one constant,his love for Ennis.His greatest joy and ultimately his undoing.