Being an introvert and having social anxiety are not the same thing, though they do often look the same from the outside. I’m introverted but do not have social anxiety. I also am perfectly capable of interacting with others, I just need some alone time to reflect after a lot of interaction. As far as homeschooled kids, many I’ve met, including some I’m related to, have problems interacting with others because their exposure to others is limited, and exposure to a diverse group of personalities is often very limited. There are ways to combat this - sports, scouts, music, other extracurricular activities, any way to get social interaction with those different than you. Once you enter the real world you will run into all sorts of weirdos. Get used to it.
As far as marriage advice, marry someone you love (should be a given), someone you trust, someone you respect…and make sure your partner loves, trusts and respects you.