Let’s start by excluding God from that question. It goes without saying that God should be your best friend. If He is not, you have more important things to work on :o).
If you answered that question with a resounding “MY SPOUSE”, congratulations! You get it! Your best friend is the person who is with you through thick and thin, mountains and valleys, joy and suffering. This is the person who you share most of yourself with. The person with whom you can be at your most vulnerable. Until you get married, that person can be one or a few other people. Once you have committed to your spouse, however, he or she must fill that role. Otherwise, you are setting yourself (and your marriage) up for failure. Your marriage is the most important relationship that you have outside of the one you have with God. As such, no other relationship can come before it. If you are sharing your innermost self with someone other than your spouse, that relationship is coming between you and your spouse. But my girlfriends understand me so much better than my husband, you say? My buddies get me in a way that my wife doesn’t, you say? We say that this is part of the work involved in being married. If you both work at being each other’s best friend, you will find that you will not only “get/understand” each other, but that the intimacy backing it up makes that relationship infinitely stronger than any other. When your spouse is your BFF, they will surpass what you thought you had with anyone else. We speak from experience here. If you and your spouse aren’t best friends, start changing that now. We promise you that God will reward it.