You are not worthless, although feeling left out certainly causes many people to feel that way.

Perhaps you are somewhat shy and an introvert? I can relate to that. Shyness can be overcome by reaching out to people in spite of any fears about it. Introversion is simply a different way of relating to people - we value deeper connections with a close-knit group of people and can be exhausted by endless, random socializing.

I believe the trick is to deliberately be on the lookout for people who share common interests and perspectives on things, actually seek them out, and also to move past the shyness. This takes practice and yes it can cause some anxiety. The anxiety gets worse the less you open up, because it leaves room for assuming you won't be accepted by people. I have been through this and am still working on it.