I haven't read all of the other posts so if I ask you something that someone else has or repeated something, i'm sorry....
It seems very unusual that your boyfriend wants to go back to having a, what seems to be a casual relationship. You two have been together for a very long time and what he says worries me slightly. When someone suggests something like this, it doesn't sound that the relationship is going to last but maybe the pressure of a very serious, very long term relationship is getting to him. You need to sit down and speak to him about the situation and talk things through. I know asking questions is going to be difficult but you deserve to know the answers, you need to know the truth.
If you aren't happy with going back to having a casual relationship then it's best that you end the whole thing because you don't deserve to be unhappy. You deserve to be with someone who loves you, someone who treats you right and someone who only has eyes for you. From what your boyfriend said, I doubt he is the one for you because all he is doing is hurting you. It's difficult letting go of a long term relationship, i've done it myself but if it isn't working for you then it's something you have to do. You will get through it and you will find someone else. These things will just take time.
Speak to your boyfriend, ask the questions that you don't want to ask because you deserve to know the truth. I hope you're ok...