It’s not BC. It’s your son, and it’s tens of thousands of sons and daughters at colleges all over the country. What he’s experiencing is common.
Please read this pinned post: http://talk.qa.collegeconfidential.com/college-life/2016222-to-those-who-feel-lonely-homesick-friendless-think-they-chose-the-wrong-school-etc-p1.html
I feel for you and your son, because I know how hard it is. Your son should try getting involved in different things that aren’t clubs. Volunteering and the campus ministry are great ways to meet people who will likely be very accepting. He can get an on-campus job that puts him in contact with a lot of people. He can try other clubs that don’t require him to try out, or whatever it is. He can go to his RA and explain what’s going on. He can join some kind of board games group. There are plenty of options.
I strongly encourage you to share these linked posts with him. Meanwhile, give him some power. Ask him what HE wants to do about it. Let him know that he can fill out transfer apps (ensure he understands all that is involved with transferring) becasue he then will feel less trapped. Ask him what will be different if he leaves BC and goes to another college. He needs to persevere, because it takes time. Good luck to you both.