If you belong to Christ and if you are striving to live out what He has called you to, then you are obligated to love your spouse more than you love yourself and more than you love your marriage. You are called to make sacrifices for your spouse just as Christ made sacrifices for you. You are called to submit all of your resources in the service of their best welfare just as Christ sacrificed all that He had in service of your best interest. Every day. And it never feels fair; your fairness meter is broken.
Spouses in good marriages report - with a wink and a smile - that they do 60% of the giving in the marriage, but they don’t mind; in the room next door, their spouse is saying the same thing. It will never feel fair. In secure marriages you don’t meet in the middle; health is characterized by a resolve to give 100% to your spouse. When both couples are thinking and acting this way, it works. Often this is the obvious stuff: changing your schedule to accommodate his, stepping up to help out with child care so that she can get a break, going out for Mexican instead of Chinese, working another year in the job you hate so he/she can go back to school, giving up your hunting weekend so you can get away as a couple.
However, it’s not always the obvious stuff. Sometimes serving your spouse’s best interest doesn’t mean giving them what they want or doing what makes them happy. That indulgence and blind grace just fosters selfishness and immaturity. So, when she asks you for that European vacation and you know you can’t afford it, then you say “No” and you compassionately hold the line. And when he tries to initiate sex 15 minutes after he called you a “bitch” because its his confused and self-centered way of trying to fix things, you refuse him until there is some accounting and dialogue about what has gone on.
And it may be that at some point - when your spouse gets lost in something that by its very nature competes with the marriage - an addiction (substance, sex, work or spending) or an affair - you give them an ultimatum. You put a gun to the head of the marriage and threaten to kill it unless they stop destroying themselves and re-invest in the marriage. If they refuse, you involve others you trust and then a counselor and then a pastor; then you move toward separation and, after a while, divorce. Not because you can’t take any more disappointment or conflict or distance, but because the integrity of your love for your spouse compels you to submit everything - even the marriage - in the service of their best interest.