Why did my partner get close to me then end it?

My boyfriend and I were best friends for 4 years and got together properly 8 months ago. We had an amazing relationship and I'm the last 2 weeks he has been even closer than ever (we were close anyway) and he started making a brilliant effort with my son, getting his spare room ready for my son when we were up staying at the weekend. We had a holiday to West coast America from Scotland booked for sept that cost a Lot of money. We had a lot of plans. He used to be married but never bothered to get a divorce as lots of people do then on Monday he heard he would be divorced within the week. He phoned me and ended our relationship very erratically. Telling me he didn't care (I know not to be true) and that he has feelings for his ex and will try to get her back. He changed his phone number and told me not to contact him again. I am more upset over the loss of friendship and my love. I don't know what to think. I think it was the shock of realizing the marriage was finally over and he isn't in control of it that had made him do this because we had one hell of a happy relationship. I am absolutely devastated. He has always been quite thin skinned and easily hurt and retreats to his shell pushing all that love him away. Thing is, spookily enough, I told him the morning he ended it that I'd had a dream he had ended it as he wanted back with his ex and he said "don't be silly, that will never happen". Then he went to work, got that phone call from her and our whole lives have changed. What can I do? Is it the shock of the divorce from a 25 year marriage with 3 kids or does he really not want me (because his actions were always loving and caring and he was always happy and said it himself).