Wow, I can tell you're upset because, like me, the words just keep on coming without pause! Now I know how my friends feel when I text them while upset, it's kind of overwhelmingly hard to read ;-)
Anyway, to try and answer your question...people are different. Some people are more social than others.
My oldest son (17) is quite popular in school and at the martial arts studio where he works and studies, but he doesn't care to have friends over very often. I worried, too, wondering what it could be about our home that made him not want to invite friends over, but we've talked a few times about it and he says that while he likes people, he just wants to relax when he's home, he's worn out from the days socializing.
My second son (12) goes through phases where he will go from constantly having friends over/being at friends houses to staying solitary in his room for a while. He will say things like "oh, i just got tired of always being around people and wanted to be alone for a bit," or "I just haven't hung out with so-and-so for a while so I plan on spending some time with them now."
My daughter (11) feels isolated if she hasn't had contact with someone outside the family in the past 15 minutes (lol, I might be slightly exaggerating!)
My youngest son (8) is not social at all, and had never cared for people, so we were very concerned with how he would do when he started school. His teachers say he is well liked and popular with the other kids, and he is invited to many birthday parties...but he rarely wants to go. He only really likes a few kids, and even them, he doesn't ever think of playing with, meaning if they invite him, he is happy enough to play with him, but it never occurs to him to invite them to play, even if I suggest it, he will often say, "no thanks, I'm busy reading/playing/etc."
These are just 4 people, from the same family, yet they are all so different from one another!
The main thing I have learned is to hope you've instilled the values that are important to you, and let them use those tools to guide them through the life they are most comfortable with.
I am not sure if I would be comfortable with the boyfriend being her main form of socialization outside of organized activities (at any age, but 13 seems extraordinarily young, to me,) but you didn't ask about that and it's a whole different post!
Good luck to you :-)