Take this as a learning curve. In future, don't reject your friends in favour of a guy or throw your whole life into a relationship. Ahealthy realationship is one where people can spend time apart and it still works. For the other person in the relationship (in your case, the guy) it isn't an attractive prospect to have the other person so wholly dependant on you, which may be where some of the realtionship problems came from.
As for now, your life is not at a dead end. What are you - 17, 18? There are a million opportunities for people your age.
You could go through clearing and get into a uni, or do some kind of higher education course or get a job - in any case, you will make more friends and meet new people.
I konw it's hard but you really have to put this out of your head while you are revising. You can have the rest of the sumer to sort your life out and you'll have more opportunities at your disposal if you get good grades.