Do not feel sadness for n52 Batman and want him have an other happiness life.
Although at the end of the story the n52 batman cannot be with the n52 superman, but their minds are connected. What separates them is death. In the end, n52 Batman asked to bury his ashes near the n52 Superman, so even if he was given a new super, would he accept?
He is using his life to love his Superman. Spend billions of light years to across the Phantom Zone just want to confirm n52 Superman is good at the new world. There is no second share of this love.
A few days ago I saw a Japanese program "Can I Come Home With You", in which the oldman's wife died of cancer when they’re young. Since then he has never married and has composed songs for his wife for decades. He doesn't drink alcohol often, but he commemorates his wife's death day each year, drinks a small sip in the izakaya, and then goes home on the white snow. Even after so many years, talking about the death of his wife before the show still couldn't help but wet red eyes. His wife asked him before she died: "Why am I alive?" He said, "Can I say that you came to this world just to meet me?"
N52 Batman didn't feel lonely in the end. He already knew in his heart that he and his Clark knew each other and loved each other more than themselves. Nobody can understand, nobody can replace in their life. It's just that the n52 Superman has already made another decision before understanding this.
I’m sorry for this miss. But that is the ending of them.