Based on my own experience, having come to the realization that my husband is more attentive, interested, giving, physically present, mentally present, emotionally present and just overall kinder and more loving for a few days after we’ve had better than mediocre sex I can believe that sex has the power to “appear to” strengthen marriage. I say “appear to” because I don’t believe that the truth about your relationship lies in how close you are in the days after sharing orgasms. I think it says more about how little you truly value each other and proves the foundation of your relationship is shoddy when lack of sex undermines the strength of your marriage and puts you at risk of divorce.
I have a difficult time being able to intellectually accept that sex should be as powerful as that because what it says to me when lack of sex destroys a marriage is that marriage is entered into as an agreement to exchange sex for commitment and love. But my personal experience has been that the longer my husband and I go without sex the more strained our relationship becomes, the less married to each other we feel. I won’t claim it’s entirely my husband’s fault. I think it’s true on my part as well that the longer we go without sex the more distant I feel, and I think it’s entirely to do with both of us having bought into the mentality, whether we realized it coming in or not, that marriage is indeed an agreement to exchange sex for commitment and love.