Why does the husband leave the family in The Others?

Here's the way I understood it:

The husband was killed in the trenches, and is doomed to haunt that place (as his wife and children are doomed to haunt the mansion). He comes home to visit his children, but eventually returns to the front. It is also hinted that his relationship with his wife was strained even when they were alive, and that this strain is what drove the husband to go to join the war in the first place.

The husband is killed whilst on the front line and just comes home to say goodbye to his family before going back to haunt the place where he was killed. He regrets going to war more than he can say, but feels destined to haunt the trenches because for some reason the 'law' is that the ghosts must haunt the place where they died (like the three housekeepers who stayed there when "All the other servants left"). The husband partly realises they're all dead and understands this 'law' of having to haunt the place of death, but can't put it into words to explain to his wife.

I also think the big thing is that he can't relate to any kind of normal life anymore after the war, even though he loves them all. I think it's that he can't explain to them what he's been though or live as though it never happened, that's why he doesn't explain why he feels so driven to leave and go back to where he feels he belongs (maybe his delusion isn't that he's alive and at home like the wife, but alive and at war, just nipping back for a home visit, even though he partly understands they're all dead but is too confused to mention it) and leaves whilst his wife is asleep because he's struggling to comprehend the situation himself.

He obviously feels his 'place' is where he died, despite the extreme regret he has at going to war. I think the narrative is that in his mind he comes back to see his family after his death to say goodbye to them forever and then go and be at the trenches (where he feels he belongs, just as the wife and children feel they belong in that house).

The old lady says

I don't think he knows where he is.

I think he didn't find his wife but the opposite (she found him lost in the mist because she needed him). He is lost in "the mist" probably because the traumatic events of the war, this explain his personality. He will never come back home, and is always lost.

I think we really don´t know where the husband went, and why he didn´t stay at home. Amenabar didn´t told us everything. That´s why the movie is so good.

We get to know (later) that all the people in the house is dead, so we can say that the husband is also dead (because he can share the same time and space). Maybe, living in the house is a form of limbo to all the family, until they decide to abandon it. To go where? An hipotetical heaven?

Nicole Kidman was afraid to many things, including the children leaving the house. This was her denial to the world, to the experience of letting go, and finally leaving the house.

Maybe the husband was not in denial, but in the uncertainty of knowking that he don´t really knows what is going on.

No. The wife and children are stuck in purgatory, but he gets to go to heaven. In some Christianity and Catholicism beliefs, suicide prevents you from going to heaven. You're just stuck. I am not 100% sure about the children, but I think their distressful death by their mother leaves them trapped.

The husband goes to heaven. The mother and children remain because the mother killed her children and herself, and the children admitted that they would openly deny Jesus the Christ before the Roman governor to save their lives.

I always felt that the husband came back home on compassionate grounds and went to the house in a state of shock and felt the spirits of his wife and children, he went just to feel and get his head around the situation, he stayed for a while and then left to grieve

I'm in the midst of watching this movie now. I just reached the part where the kids deny their belief in the Bible for the second time. You will recall they said they would deny Christ, like Peter did. This time they said they didn't believe God created the world in 7 days, nor that Noah only had one boat for all those animals, nor that the Holy Spirit is a dove. THEN, Mrs. Mills asked them if they had told their Mum. They hadn't. Perhaps, then, the kids did not get to heaven for two reasons (both of which y'all had mentioned): first, I'm only half way through the movie and they have denied God's word twice already; and second, because they haven't told their Mum their beliefs, so they are stuck with her, wherever they are, because they don't want to be truthful, or they don't want a division between them and their Mum.

The children had not had their first communion yet, which would mean they are not officially Catholic, meaning they could not be allowed into heaven. It's a very big part of the story line, if something is mentioned that much in the narrative then it is very important. The mother was a suicide and had murdered her children. The father did not answer his daughter when she asked him if he had killed anybody but when she spoke of it later she said he saw many dead bodies. The servants are there not because they are haunting but because their purpose is to help the family realize their deaths. The state of the husband is ambiguous, but I believe he may be alive. When he was found in the fog he said "sometimes I bleed". If he were dead, he would not bleed. If that were the case, you would see the state of the dead. I believe he came back to visit the graves of his family and is in a state of mourning and ptsd and used the war as way to gently let her go since she had yet to come to terms with what she had done and thusley had yet to be able to see the people living in the house. I think the people living there were kind enough to let him stay and say goodbye, out of kindness and perhaps hoping that it would be giving the spirits closure and make them leave. It seems that the people could see and interact with the ghosts as long as they were willing.

Maybe they're all in limbo. The mother for killing the children, the children because of their trauma and unwillingness to leave their mother, the servants because they were not "believers" and the father because he was a soldier. The children ask how you know who the "goodies and the baddies" are in a war. The lines are so blurred that when he went to war and was killed, he was stuck too. Because he killed others. OR there is no heaven or hell or any of it and ghosts simply haunt the place where they died. However, that doesn't explain the people in the book of post-mortem photos. I would have to assume that SOME of them died in the house in the past. So where are they? Why only 6 ghosts in a house with such a long history?

I always thought it may have had something to do with him being sickened by the way in which his wife and kids had died.

I think that the husband was just in a coma, and needed to go back to the front because his body was there, and it was time to wake up.