Not many people have taken this stance so far, but I'm going to say it anyway.. NEVER, EVER choose a university based on where your boyfriend/girlfriend/friend etc is going to go. It's too important a decision.
Being 100% honest, your sixth form boyfriend will most likely break up with you before the end of first year, as university changes things massively. He'll meet new people, as will you, your schedules will be different. Having a boyfriend in sixth form is easy as you can be sure you'll see each other every day. Uni brings other pressures, and makes things difficult.
My best advice would be to go where YOU want to go, and take the LDR route. I know you say you don't want to do that, but if your relationship is strong you will get through it. You can visit each other at weekends or in the holidays and even some evenings sometimes depending on how far away you are from each other. You can pretty much travel the length of the country in less than 3 hours on a train, so it's not really going to be much worse than that.
I know you think your boyfriend means a lot to you now, and perhaps he does, but your lives are going to change as soon as you leave college, meaning you really shouldn't make these decisions based on him.
I might well be wrong, and you may have a strong relationship - but if that's the case then it WILL survive wherever you go.
Just make sure you make the right decisions for the right reasons.