The Torah forbids taking back a wife if she married again after her divorce. If she wasn’t married, only betrothed, then its fine, no issur. The flow of the p’sukim seem to indicate that the situation was such that was no intention of exchanging wives here. Rather, the second husband simply hated her and divorced her, or that he died. So what’s the issue, why is it forbidden for her to go back to her first husband? We suggested that perhaps the matter here is that there are too many issues involved here; the first sour marriage + the fact that she had a relationship with another fellow + the breakup of that relationship and the coming back to the first husband. This all makes for a too complicated situation for marriage. The two are ruined, “hutam’ah”, for each other. There are too many issues, and issues within issues, for the marriage to be successful. And in our own marriages; resolve issues before they become too many and too big to resolve!