First of all, thank you so much for your service.
Now - school adds a lot, particularly when you're older (I went back and got a degree last year, and lemme tell ya, concentrating is not easy and I did it without kids in the house. Can't imagine what that's like with them around). So even if it's not physical, it's rather mentally exhausting all the same.
Your whole house dynamic sounds difficult. Have you (either or both) been to counseling? It might help, not only to unburden yourselves about your marriage but also about how things have been changed radically by your injury. Even if it's been a few years and everybody's used to it, that doesn't mean it's all said and done.