Cailin, lots of things.
DH has always hated his job, but it was well paid. Lots of stress and responsibility. He wanted me to stop work when DD came along but suffered with the burden of supporting the family doing this job he hated. He was grumpy and miserable, took it all out on me, very critical. I was lonely at home with little ones, especially after we moved to somewhere away from all our friends (for schools and to not live in London). I got depressed, low self esteem. He only had energy for work and the children.
I wanted us to go for counselling, but he refused and didn't change and become more supportive until I'd got to the point I was saying I wanted a divorce (about 4-5 years ago).
We are also very different in many ways and there is a big age gap (he's older). I always felt like the junior partner and felt torn because I didn't like being 'kept' but wanted to be at home with the children when they were small as well. But not much appreciation of everything I did to try and be a great wife and mother. The classic story of a SAHM who gets no credit for the job.
I started a demanding Uni course leading to a career when kids were a bit older and that made us grow apart. I also fell in love with someone else, 'nothing happened' or was even said but the feelings were all there at least on my side.
I haven't been very nice to him in the last few years, because I'm angry at how he treated me earlier on. He blames me for our problems and is unwilling to accept his part in it.
Also, his job was very well paid but his business is now failing because of the recession. He's always very stressed re money and I feel powerless. I'm too far down the line to give up my course, but won't be earning for two more years. So lots of pressure there.
We have no sex life, it got worse and worse because of the problems. I stopped wanting it, rejected him, he stopped seeking it - a vicious circle.
But on the positive side, we have wonderful kids that we both have a great relationship with. I'm wondering if we move on to a new house, which would take the pressure off (we'd bank enough equity to mean he could do a different job, even no job for a while) while I qualify, things might be different. But it's a huge mountain to climb and I don't know if it's possible. But the alternative is grim too. The kids are his world and he would lose them for much of the time, he would also lose a lot of his 'wealth' and be in a dire position if his business fails. I don't know if I can live with that, it's not what I want for him. And I feel a profound sense of 'failure'.
Sorry for the essay, but you did ask! That's actually a simplified account. All marriages are complicated, aren't they?