I personally think it was so clear that Damon will try and save everyone that he can. He doesn't WANT anyone to die.
His 'I hope so' to Elena made that clear.
I also think the writers wanted us to see that he HAS come to care about the others. I think we've seen it before with Caroline...and then this ep with Bonnie. He's not super expressive about it. But he DOES care.
What he was saying with the 'I will always choose you' is that at the end of the day, IF it comes down to a choice, and he can't save everyone, Elena is his priority.
He is in love with Elena.
I really don't understand why people seem to think he shouldn't feel this way? Why would he save Bonnie, or any of the others over Elena? Ok, she might want to die to save everyone...but her reaction to Damon's words showed that she understood.
For example, Bonnie would let Damon die to save Elena. But Elena has expressed before that she'd also die to save him. So it works the same for all characters