In desperate need of advice

[Coolschmool]

Hello all. I am not sure where to turn to, for I've tried to talk to multiple friends for advice, but even their advice doesn't feel sufficient.
My boyfriend and I were together for just over two years. He is 17 and I am 18, (19 in a couple of days).
I once was very insecure and would be very negative on myself and my boyfriend was very optimistic and positive and nothing ever really got him down. All of a sudden, a few months ago, we switched roles at basically the same time. I feel very confident in myself and generally optimistic. My boyfriend started getting into poetry and reading and became very interested in the other side of life, that being "feeling miserable". It's very hard to explain, but my boyfriend claims that he feels miserable, but fuller than he has ever felt and that he is just in a downward spiral and becoming more miserable. From result of this, he has become very interested in his education and took up many classes for his senior year to fix his GPA in hopes of getting into a university. He became very stressed from this and would take out his anger on me or his mother and father. He has always felt that his parents were over-controlling, so he has also taken up smoking cigarettes as of a month ago or so, which he used to want to do, but wouldn't because he knew it would hurt me. It did hurt me, but he decided that he wanted it to be his own decision.
He was always extremely clingy towards me and would tell me that he could never love anybody else and that he wanted to marry me. Even as of a few days before we broke up, I had gone on a trip recently and he claimed he was going crazy the entire time and he had a miserable week missing me and continued saying he wanted to marry me.
A few days ago I called him while he was with his friends and I guess he was just "thinking a lot" and said that he needed time to think things out. The next day I called him and thinking that this is what we both wanted, we broke-up and planned on being best friends. I thought that it would all work and that I would be totally fine by being best friends, but I spent time with him, I was miserable. I want him back more than ever and I know I made a mistake and agreeing on breaking-up. I can't seem to be around him and just be his friend. All of the online advice claims that I need to ignore him in hopes of making him miss me, but there are commitments we have made where I have to see him, such as going to Florida in a month with his mother and brother. I am very close to his family and they have done a lot for me in the past two years and I don't want to give any of them up, especially him.
I have told him that I am miserable and want to make things work, but he just repeats "I can't do that right now. I can't be in a relationship right now." He says he still loves me and has feelings for me and wants me in his life, but says he can't be positive we will ever get back together because he "knows" that he's not getting any better and going in a "downward spiral". I just don't understand that so recently he was telling me he wanted to marry me and that he misses me whenever I am gone. I fell like he's not even trying to save what we had and I on many accounts fought very hard to stay with him when the times were difficult. Basically, I am wondering if he will change his mind or how I can make him change is mind, etc.
There is so much to write, but I feel this sums it up in a basic way. Thank you for any advice you may have for me.

[steviej]

Age is against you, he's still maturing and changing, there is nothing you can do about that. Give him as much space as you can, go no contact for as long as possible and see how the situation is then.
I'm sure his family would understand you not going on the trip if you and him are not longer together!

[Coolschmool]

Thank you, Stevie for your reply. I know why young relationships fail so often is because people grow up so much during these stages! I never used to realize that when I was younger at first in our relationship. I'm going to try no contact as hard as I can, hopefully I can stick with it.