1) Learning about Attachment Theory was a breakthrough; it explains everything about my behavior, relationships, and life choices. It also suggests a method for change and ongoing personal development. Here are some books on Attachment Theory:
2) It's harder to make friends as you get older. Most friendships are built on an ongoing shared experience that is challenging, such as being in school together. Most of my adult-onset friendships are a result of having worked in small startup companies that were struggling to survive. Casual meetings of potential friends are much less likely to generate the energy and commitment for developing a friendship. If you're interested in the research on this, look into the work of Robin Dunbar, e.g.,