This is Tony Isaacs, thank you for your question. The answer is fairly simple. God designed it to be that way. Two become one flesh in a marriage relationship based upon love and commitment for a lifetime.
“Two become one”
‘For this reason a man will leave his father and mother and be united to his wife, and they will become one flesh.”
Oneness is designed for a lifetime
Matt 19: 4
"Haven't you read," he replied, "that at the beginning the Creator 'made them male and female, and said, 'For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh'? So they are no longer two, but one. Therefore what God has joined together, let man not separate."
Love is demonstrated in a husband/wife relationship by commitment, hence the marriage vows and a public commitment. I personally don’t know how you could turn off your love and commitment towards a mate in 7 years unless you enter the marriage with a “conditional love” or allow “sin” to dominate the relationship. That would be totally opposite in how God designed us for marriage.
Christ’s love toward us was unconditional and sacrificial.
“…In this same way, husbands ought to love their wives as their own bodies. He who loves his wife loves himself. After all, no one ever hated his own body, but he feeds and cares for it, just as Christ does the church”.
And we know that Christ was willing to die for our relationship.
I am very grateful for God’s unconditional love. There is no time limit on that.