Thank you for your post. I understand your position, I have had friends in the past who would do this kind of thing and I accepted it as normal until I found a new normal, and realised that it was wrong.
I would recommend talking to somebody about this (a therapist, psychologist or helpline, as smallwolf has suggested). Sometimes talking to somebody can be a great way to consolidate your experiences and relieve yourself of any repressed emotion.
Your post really resonates with me as somebody who struggles with fleeting thoughts of inadequacy. In general, I've noticed that a lot of people have reservations when it comes to making friends or talking to new people, due to fear of failure or rejection. While humans are sociable creatures, we also tend to be nervous creatures as well. Particularly in situations where you and a group of other people are/have been in a similar position, like starting a new job or studying at university, it may be reassuring to learn that most people are feeling the same way and may even be shy to talk to you as well.
As always, it's important to remember that you are worthy of love, respect, and feeling like you're more than enough. If you happen to make friends with people who do not respect this, it's perfectly reasonable to end the friendship. There will always be people who are willing to support and accept you, it's just a matter of finding them.
I wish you all the best, and please feel free to get in touch with us again if you have more to talk about!
Kind regards, SB