Whether or not your social life gets better depends on a few things - obviously if you are going to be on a very intensive course with high expectations of you workload-wise, it will be different to a "lighter" course.
Speaking VERY generally, chances are it will be better. Often sixth forms have stupid rules like expecting you to be at school all day even when you don't have lessons etc. This is actually counter productive as chances are you're too busy feeling ****ty you have to be at school to bother picking up your books and getting on with coursework etc. Obviously at uni, there won't be that expectation. Your free time is your own and you will be trusted as an adult to use your time responsibly and to create your own work/life balance, on the condition that ultimately, if you get pissed all the time and never do any work, you will be the one to pay for it via your grades - no one is there to babysit you. Also, you will find on MOST courses that you will have far less hours than you have currently per week. In my first year, I think I had about 8 hours a week of lectures and maybe 5 hours a week of seminars, so when you think about a whole week, that's a lot of free time, even factoring in your homework.
As for the friends thing, it will get better. Unless you went to a really traditional uni, you will find you'll be mixing with a lot of different people from all walks of life and will probably be living in halls with a diverse range of cultures and backgrounds. In my 1st year, every single person I lived with was a different nationality and a real mix of how well off we all were, so it was great! You'll also find unis usually have what they call a student union which is a club on campus for the students which will have theme nights etc and unis usually put a lot of effort and money into arranging social events for students. As long as you make the effort to get chatting to people and get to know them, you will have ample opportunities to meet new friends.
My advice would be - I've been there and I totally know what its like - I only had the 1 friend by the end of college and thought it would always be like that. Just suck it up, get through it, focus on your exams...and then when it comes to first year you have a lot of living to do! Work hard play hard!