When a relationship ends, the one who was loyal remains single until the wounds that left the damage are healed, the other immediately enters into another relationship.
This has a simple explanation: They are looking for a partner quickly, because they do not know how to be alone, they are people who do not know how to love themselves, they do not know how to wait, they are simply looking for someone to fill them spiritually because they are empty. In short, they go through life destroying hearts because their emotional maturity and lack of self-love mean they can not cope with their loneliness.
Many times we shield ourselves in what they say there, that a nail takes out another nail, beware that the new nail ends more by sinking the previous nail and you end up more hurt. Love, love and do not hurt.