You have a lot going for you. People like you and respect you. You are intelligent. Best of all, you have a sense of humor.
Being alone and intimate with someone takes a whole different set of skills than leading a group. A secret that a great many very well-known and successful leaders and celebrities share is, if fact, how shy they are. You probably didn’t develop some important skills for being one on one with people because you are by temperament kind of shy. It’s time for some remedial work. You don’t have to turn yourself into a social butterfly but having more than one good friend (as you already found out) is a good idea.
Learning friendship skills is really no different than learning anything else. Do some reading. Watch other people carefully to see how it is done. Find yourself a mentor. And, here’s the hard part, take some risks. If you are feeling awkward, you can share it instead of bluffing or running away. Most people respond with sympathy and are willing to help out. I know several people who found true love by figuring out who the other shy person at the party was and connecting around how hard it was to be there. You might also look for a therapist who runs social skills groups. In the safety of the group, you can try out new ways of relating and get feedback from others who are struggling with the same issues.
Working out has probably shown you that practice plus time plus being willing to push yourself some equals improvement. Social “work outs” are no different.
I wish you well.