Pulling up a cushion.... Been there with my DS, now five, finished bf when he was 3 1/2.. It was heartbreaking when i made the 'decision' a year before and simply couldn't cope, i ended up (hate to put it this way) stuck for another year, and it made me grotty, tired and resentful of him.
So you are doing entirely the right thing. He will still love you, you're a wonderful mum for doing it this long
I know you don't feel that right now though <Unmumsnetty hugs>