Some people believe any narrative they tell themselves. No matter how unhinged, crazy, irrational, or downright untrue something is, sometimes someone just wants to believe something false, even if it's a hard idea to swallow. It could be the end of a relationship, and skewing the situation to see your ex in a bad (or good) light, undeservedly. It could be convincing yourself someone's against you, that you're better at something than you are, it could be accusing your friend of being with your husband.
This particular story blows my mind. Not only does this woman accuse her friend of being with her husband, but she insists that her friend's baby is her husband's baby, demanding a paternity test. My question is, why did the husband get this idea into her head in the first place? It's in no one's best interest to convince your wife that your friend's baby is actually your own, knowing full well that you two have never done anything together. Read this wild ride of a friendship that went downhill quickly.