The situation you find yourself in currently must be taxing. It reads like your wife has moved on from the emotional side to your marriage but, I assume, you being away for such long periods, it would be more convenient for her to remain in the home with your childrens lives not disrupted.
Unfortunately your sacrifices for your financial stability, dedication to your work and so on wont compensate for other things that she is finding difficulty with. The only way to find this out, if it doesn't come from her, is during counseling.
Have you considered leaving your job and finding a job near home? Only you would know that challenges of such a change and you also know how far your marriage has eroded, so such a change might not be to your long term benefit.
If you feel your marriage is taken its toll on you mentally and it does seem that way, have you considered renting a place nearby the family home so when you return your children can visit after school and you could rebuild yourself a life. Children are resilient and will adapt to the new arrangement. Your wife can apply for help through human services but you would be required to pay child support via the rules or meet an agreement with your wife.
That all sounds negative but you don't describe your relationship in a positive light. That leads to making changes that is for the best of all parties concerned.
If ever you feel distressed about any of this you can post here or you can contact "Dads in distress" just google them as well there is lifeline. As you know you have 4 kids that need you and having been in your position myself I know how low you can get under such duress.
For me, back in 1996, I was devastated when my marriage folded and lost for 3 months before I found a block of land and built my own home. Such action led to my focus on that building that was distracting me from what I'd lost. So finding a new direction is paramount in your healing.
I hope you are ok. Repost anytime.