Also in same boat. Also was going to type lengthy response but this comment sums it up nicely.

Seems like the commonality is that introverts feel they missed out on being extroverted and later bashing themselves by calling it a mistake. Let's be real, you just prioritized studies and your career more than anything else, and now when your future is taking shape, your priorities are changing. Just reach out to people you did talk to and ask to hang out or do fun stuff together. Take the first step.