Surely everyone has at least once encountered a rather strong and not entirely understandable feeling of jealousy towards the former partners of their loved one.
Some take control of their feelings and stop becoming hostages to their own jealousy of the past.
It is worth remembering that we are highly dependent on our genetics and "ancestral memory". Previously, people mostly knew 1-2 partners throughout their lives, so they had no reason to be jealous.
Nowadays, many people by the age of 30 have such an impressive “track record” that it raises doubts about their fidelity and ability to create a family with one person.
If your loved one was not the initiator of the breakup, then there will always be doubts about his feelings. After all, if the ex-partner had not left him, then you would not have even met.
Sometimes loved ones themselves create the ground for this jealousy. For example, they keep gifts and joint photos with exes, look for them on social networks, correspond.
The past must remain in the past so as not to destroy the relationships that you have here and now.