Hi xobabylovelyxo & welcome.
My first response to the book was 'no', but then I thought that there is a lot of very helpful information in books, so I'm not sure. I wouldn't buy a book that I couldn't check out first, though.
As ever, without really knowing the people or the situation it's difficult to know how to respond.
There could be all sorts of things going on here.
You have been together for quite a long time, and from a fairly young age. Some boys, especially if they see the relationship lasting, might start to feel that they need some space, and some time apart, before they feel ready to settle down.
It's also possible that, while you feel that he is 'the one', he may feel that he has moved on, and saying that he feels that you are incompatible is his gentle way of letting you down.
Yet you say he is open to you getting back together, so I'm just not sure how to interpret that.
Actually, many men & women are incompatible, when you think about it, because our brains are wired differently.
There are books on this subject, and, while I wouldn't necessarily agree with everything the authors say, it really is worth reading up about the subject, because this can really help with misunderstandings, arguments, etc.
I would recommend that anyone in a heterosexual relationship should read about this. It could enhance a lot of relationships, to understand how the mind of the other person might work.
The Venus & Mars books are some, by John Gray.
I've noticed that he has a website:
http://www.marsvenus.com/I am not suggesting that you get involved in any of his courses, or anything, just borrow his book from the library & it will make you think about a few things.
Here's the book:
'Men Are from Mars, Women Are from Venus: A Practical Guide for Improving Communication and Getting What You Want in Your Relationships'
http://www.amazon.com/Mars-Women-Venus-Communication-Relationships/dp/006016848XYou can read the reviews there, too.
More info here:
http://en.wikipedia.org/wiki/Men_Are_from_Mars,_Women_Are_from_Venus
Here's another one:
'Why Men Don't Listen and Women Can't Read Maps: How We're Different and What to Do About It'
by Allan Pease & Barbara Pease
http://www.amazon.com/Dont-Listen-Women-Cant-Read/dp/0752846191http://www.amazon.com/Dont-Listen-Women-Cant-Read/dp/0767907639'Why Men Don't Have a Clue and Women Always Need More Shoes: The Ultimate Guide to the Opposite Sex' by Barbara Pease & Allan Pease
http://www.amazon.com/Dont-Have-Women-Always-Shoes/dp/0767916107/ref=pd_sim_b_1/002-4574736-9800810Why Men Lie and Women Cry by Allan Pease & Barbara Pease
http://www.amazon.com/Why-Men-Lie-Women-Cry/dp/0752847279/ref=pd_sim_b_2/002-4574736-9800810And this one:
Brain Sex: The Real Difference Between Men and Women by Anne Moir & David Jessel
http://www.amazon.com/Brain-Sex-Difference-Between-Women/dp/0385311834Also:
http://news.bbc.co.uk/1/hi/magazine/6683241.stmThere are a number of these books about. If you go to those Amazon pages, you will see others recommended. Check some out at the library.
As for your relationship, I think that, while it's worth being sure that he knows that you consider him to be 'the one', yet you should also let him know that you are willing to give him his space. Then just see if that is all he needs, or whether he actually feels that he wants to move on.
Maybe a letter, setting your thoughts out, but not putting any pressure on him might help?? I should read one of those books though ~ it really could help you to sort out your thoughts.
Good luck!
