Their insecurities make them fear losing you to others.
But if they always tell you they don't like your friends in order to discourage you from spending time with them, then it's manipulative and you need to discourage it.
Adults who chose statement A above, for instance, were classified as individuals are easy to get along with, and good at resolving relationship conflicts.
Other children had an anxious/ambivalent attachment style—they became visibly upset at any separation from their mothers, and seemed preoccupied with possible abandonment.
If you love your partner and want to work things out, then you need to understand where the insecurities are stemming from and try to help them let go of the unnecessary worrying.
But, if it doesn't stop and becomes too much for you to deal with, then you might need to end things for good.
It is normal to be curious about the past, but not to an extent that it becomes an obsession.
An insecure partner often wants to learn more about your ex because, mentally, they are constantly comparing themselves with the ex and trying to figure out if they are good enough for you.
I find it relatively easy to get close to others and am comfortable depending on them and having them depend on me.