I'm truly devastated and heartbroken. Grass is not greener?

Was with my boyfriend for five and a half years, just moved in together. Very loving, stable, trust worth relationship with hardly and bumps or arguments. Things were pretty much picture perfect, I couldn't ask for a better relationship.

Only recently moved in, talk of marriage did come up, when your with someone that long its inevitable what the next step is but there was never any pressure etc.

Within the last two weeks of our relationship he became distant and we split because he said he needed space and wasn't sure if he was in love with me anymore but he still loved me. considering we had just had an amazing celebration in Rome of our anniversary, he was cooking me candlelit dinners, he wanted me to move in and was so excited about it. Within a month he was seeing someone else, they have been in a band together which started a few weeks before we split...i knew she liked him and obviously gave him a lot of attention which he took to and at the moment thinks she is the best thing since sliced bread. Although she is DEFINITELY more into him and is totally infatuated and his ego is out the door right now.

He never cheated he split up with me because he obviously felt guilty about the way he felt, and then within the few weeks following they started hooking up...i don't understand how you leave a relationship like ours and suddenly jump into another with someone who he has barely anything in common with and is 7 years younger. He says to his friends that this new girls isn't half of what I am and since they got together (2 months) he has dumped her 4 times saying he still loves me and was confused stringing us both along. He told me friend I was the most important person in his life? (I don't think he understands that I won't be part of his life anymore)

I gave him a final chance after he admitted all this to me and said he made a mistake and has messed everything up but he has gone back to her saying he likes her more than he let on. I have cut off all contact . He says how sorry he is but I don't believe him, I don't think he truly regrets it not yet anyway. For the last few months he has had his cake and eaten it. Its so sad to see him like this, he is losing respect from all his friends ( our friends) its like a quarter life crisis.

I'm going to get on with my life but I'm truly devastated and heartbroken. I think within the next year my phone will be ringing and he will TRULY regret what has happened and that he threw the best thing away. Its like when your right there in front of them they can't see what they have. She will never be me and once the "honeymoon" has died I hope it hits him so hard.
I'm truly devastated and heartbroken. Grass is not greener?
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