Should married couples stay in touch on a regular basis with an ex-boyfriend or ex-girlfriend? And what if the friend is also married?
Does a person's likes and dislikes in particular personalities change just because they become married? If I really enjoyed golf and had a group of friends with whom I golfed, do I drop the friends because I'm now married?
Suppose a person dated another for a period of time, but during the course of that time learned that the person he was dating was not the one he wanted to marry. Often times the ending of relationship leaves hard feelings and the people avoid each other; after all, few people enjoy being rejected. However, there are times when the decision not to marry is mutually apparent. In some of these cases, the dating is called off, but the people involved still like each as friends. That is unlikely to change just because they have gotten married.
Still, there are other factors that often drive friends apart. Single people are foot-loose and fancy-free. They are able to do things on the spur of the moment. Married couples have obligations and they find their priorities changing drastically. As a result there is a natural tendency to loose touch with old friends who no longer have things to share. But it is no problem because we build new relationships with other people who do share our core values and concerns.
It sounds as if you have one of the rarer situation where two old friends changed their position in the world about the same time and thus are able to continue a friendship.
I strongly suspect that underneath this question is jealousy. Jealousy is the strong desire to hold on to what you perceive as belonging to you. It can be a righteous attitude if what we are jealous over truly belongs to us, but more often than not, we are jealous over something to which we have no claims.
If this past friend was trying to seduce your spouse or to break up your marriage, you would have the right to be jealous and ask that ties to this destructive influence be broken. But such doesn't sound to be the case. The old friend has his or her own marriage. This doesn't sound like a person trying to break up your marriage. Think of it this way: there is a reason that other person is an ex-boyfriend or girlfriend. There is a reason why you are married to your spouse and he or she is married to someone else. That your spouse and this other person were able to maintain a friendship despite a break up shows some remarkable qualities -- qualities that you probably saw yourself and liked in your spouse. But now that you are married you want your spouse to change?
Newly married couples, especially the wife, often go through a phase where they think that they are more than their spouse's companion. They begin to see themselves as their spouse's sole companion. Anything or anyone that distracts their spouses attention from them for the least moment. Jealousy can easily become uncontrollable."Wrath is cruel and anger a torrent, but who is able to stand before jealousy?" (Proverbs 27:4). What develops is a lack of trust. You lose your confidence that you hold your spouses love -- not because of any actual evidence, but because you imagine that something might happen. That nagging doubt tears you apart and tears your marriage apart. That is why in the definition of love we find, "love is kind and is not jealous" (I Corinthians 13:4).
You have the right to be second in you spouse's sight (God always comes first), but that doesn't mean there isn't room for someone to be third, fourth, and fifth. Friendship and love are things available in unlimited quantities. There is more than enough to dominate a marriage and still have room for others in your lives.