Uni does put a lot of strain on long distance relationships. It's quite common to see people come to uni being in relationships with people back home and break up shortly after. From what I've seen it's generally the people with very strong relationships who tend to be able to do this so if it was anything meaningful it would have made it basically. It's pretty brutal sometimes but most would agree it's for the best at the end of the day.
To be honest my advice would be not to consider your boyfriend or your family unless you are caring for them in some way. Your family is always gonna be there. You've grown up with them for ages (I'm assuming you're at least 18) and after 3 years you can be back anyways.
As for feeling guilty - don't. It's only 3 years of your life and you are doing something quite useful. Degrees used correctly can give you access to loads of really good oppurtunities and accelerate your career. Additionally, there are 2 million-ish students currently enrolled at uni and a bet a large majority of the parents and parters of them don't think they are a POS for leaving them for a bit to go to uni so chances are you probably aren't either.
It kind of depends on what course you take that dictates how much you get to go home. If you have a lighter workload you might be able to go home more often. Choosing between the uni's will be a very personal decision. You will have to decide whether you value the experience of living in a nice city or the course more. If I were you I'd research what the cities are like and how they compare. Also consider how much work you will have. If you are on a really busy degree you might not be able to see the city a huge amount and you will spend a lot more time on your course so you might decide that the course is more important in the end.
As somebody who was basically a hermit crab I too was very scared from living away from home. At the end of the day you are going to move out at some point. If not now, it will be later and uni is a great time to experience this and pick up some new life skills. As for many people it might be a bit crap at first however, in the end a large majority of people end up really enjoying uni. I know I was definitely terrified of moving away from home at first but eventually you settle in and most people agree it's really good fun.
My opinion if it matters is Brexit. Get out and go uni. If a severly ret4rded and autistic guy like me can live away from home and make friends you definitely can too.
Feel free to ask me any other questions. I'm more than happy to help.