I agree you (OP) must work on developing a positive view of yourself. Maybe therapy. Don't overlook clergy even if you're not religious. Religion is as much about fellowship and how to live a fulfilling life as it is about worship. Some churches (e.g. unitarian) are quite inclusive and are much more spiritual than dogmatic.

But you will find it much harder to attract friendships if you come across as needy or wanting to unburden a lifetime of problems on your new prospective friend. Not to say a longtime friend can't eventually handle some of this, but it's not a good way to start off.

I would say avoid groups that are focused on personal success or networking. These tend to be full of people who are looking for an angle or benefit for themselves, not people genuinely trying to develop friendships and connections with a community.

I'm a highly secular person and I see people constantly say things like "spiritual but not religious/dogmatic" and I cannot figure out what that is supposed to mean. What does it mean?