When I think about what Robbie had to go through my heart breaks in million pieces...
He is the main reason I can't bring myself to forgive Briony, in any way, shape or form. Everytime I try to understand her a little bit, I remember the hell she put him into, and it's really impossible to accept what she did.

I agree with Mylan and Sophie that Robbie was very detemined to return. The way he says "I will return...our story will resume" is very determined, like he would never admit another option. When he sees his mother, even being delusional he was adamant about it. The way he says "...and she loves me. She's waiting for me" is so full of hope...
And even when he was almost dying, when Nettle tells him about the ships returning, he smiles a little bit. I'm sure that Robbie died convinced that he would be in one of those ships (altough I have another way to interpret that scene and I'll talk about it later). And, btw, that's the same perception we get from the novel - even on his darkest hours, he never gave in on hope.

In a way I think that, since Robbie was wounded, he started to live in some delusional world. Maybe it was the effect of his illness, but also that he knew, in a way, that his was a serious case and there was a possibility that he wouldn't make it. So he chose irreality over reality. Maybe, if he had told Nettle and Mace about it, they would have helped him search for some medical aid - even if he couldn't be cured, was there a possibility he would survive long enough to at least return to England and die near Cee and his mother? Oh, well, who knows...but maybe, refusing to think that he could die, that he had to return to Cee, that it was the only possibility after all the horrible things that had happened to them, allowed him some illusions to deal with his own awful reality...

And since we are talking about reality vs irreality...here's the interpretation of Robbie's final scene I wanted to talk about. The other day I was watching again (on You Tube, because the dvd wasn't released here yet) the moment when Robbie has the "reward" nightmare and Nettle wakes him up. Robbie says something like "Thing is, I've decided to stay a little bit...I'm meeting someone and I'm always keeping her waiting..."

What do you make of "I've decided to stay"? I've never thought about it much, even though "to stay" is a contradiction to his wish "to return". But following Robbie's delusional logic, since Nettle told him the cottage "is here", and Robbie believed him, maybe he thought he was really there after all and this time he had to wait for her, because Cee was the one who was always waiting for him? Something like "She said she would meet me at the cottage by the beach and now that I'm here I can't leave..."
When I thought about it this way the scene was even more poignant...