It is really difficult isn’t it? When I was at university I had a friend who wanted to spend all day, every day with me. I enjoyed her company, but had other friends that I also wanted to spend time with. Being much younger and less mature than I am now, I decided to be honest with her. I tried to do it as gently as possible, but she was terribly hurt. I am not sure that you can be honest in these situations, but there are other steps you could take to maybe have smaller and more manageable visits which would not offend your friend. Next time you make arrangements could you say something like, “I really wanted to see you to catch up, but I have an appointment at … so we will have to cut it a little short today. I didn’t want to re-arrange as it’s been too long, so I thought we could have a quick catch up today. Might that work?