[sparker72678]

I'd say start by researching attachment theory^1 and attachment styles.

Here's the gist: Children need to form secure attachment bonds to their parents/caregivers at an early age. To the extent they don't get that, they form habits, assumptions, and adaptations to compensate. Those habits/assumptions/adaptations tend to persist (because we don't even realize we're doing them) and cause problems in close relationships in the future. By learning more about yourself you can start to see those patterns in your own behavior and learn to change them.

Beyond that I've found many of the emotional regulation exercises that are a part of CBT to be very helpful.

I've also found Enneagram to be very helpful in studying myself. It's not a particularly scientific framework, but it can be a helpful lens for identifying patterns of behavior, and realizing that other people are very different, with different assumptions, thoughts, and feelings, all of which are perfectly valid.

1: https://en.wikipedia.org/wiki/Attachment_theory