I understand completely. I think I disliked the "good natured tag-along" the most out of all IEI descriptions. I do not find it to be an accurate assessment of what IEI people I know are actually doing., They tend to have a more diverse group of friends and a lot of them still feel like outsiders even in their own groups, sometimes in their own families. That is my real world experience anyway. I am no one's sidekick.
All the negative self-talk is draggin' you down and holding you back. It's hard but you need to fight your way out or wallow in self-pity until you have had enough. I chose self-pity for awhile but I learned to keep my eye on the prize, whatever that prize may be and it helps me get out of bed in the mornings. I am in therapy of course so I have had help. I do not see those negative things in you. I see someone with a strong will and determination and you want to change. That is an important step, wanting it... You are way more self-examining than I was at your age.