In the Vorkosigan Saga by Lois McMaster Bujold...
A lot of this one is about Mark since Miles is rather out of commision for big chunks of time! Mark is trying so very hard to do something important, to gain respect, to be worthy of something. So he tries to become Miles again (or rather the Admiral) so he can use those resources to save a bunch of children and maybe if he saves them they'll look at him the way everyone else seems to look at Miles.
Things do not go to plan and Miles ends up having to swoop in and save the day (or try anyway) which I think almost makes it worse for Mark, that he just can't seem to do anything right and needs saving by the "big brother" he's trying to impress. And then being at least somewhat responsible for what happens to Miles while Miles is trying to save his butt.
Mark does end up back on Barrayar and finally meets the rest of his family. He's of course expecting them to hate him, but then he had been primed with all the stories of how evil they all were. He does start to figure out that he could have a place with them if he wants it, that they'll accept him. He just has so much baggage going in and it takes so much for him to trust any of them.
And then there's everything that happens when he goes to get Miles. All of which just made my heart break for him.
But I think he does finally start to figure out who he is apart from Miles. That he doesn't have to be a better version or the backup version, that he can just be himself.