Actually I don't think you have done anything "wrong", just keep yourself open to whats possible. Sounds like you have had what you wanted, it just ended (which usually sucks).
Personally, I don't make friends and then lovers. Or at least its rare, for me the sexual component always comes first. My wife, for example, I picked up in a bar, and was supposed to have a 2 week stint of sex with. 13 or so year later and we are still together. I make connections via strong sexual components.
Limiting how you meet people is where I see the bulk of the problem in poly. I look at poly like any normal relationship. In fact my quad is really just a family, not labelled, or dramatic.. just a plain old group of people who happen to have some degree of involvement with each other. I treat how I meet people and what I do with them EXACTLY like when I was single or "swinging" (I only say swinging because I got my start as a relatively successful unicorn hunter looking for sex). That way I am not outside of my comfort zone and enjoy the interaction. That confidence is what has always helped me.
All the extras were a wash for me. OKC sucked, fetlife sucked.. I do better in person meet and greet style. Its my strength. too much emphasis it put on how different poly is.. when in reality, its just a relationship or series of relationships in some really fun structures.
Welcome to the forums.