Weary of being the father figure in little brother's life
Your role doesn't extend to reuniting your brother and father, though. They have to work this out (or not) for themselves. Ben's answer at the moment is clearly "not," so accept it and affirm that it's his decision to make.
Certainly you can suggest he keep an open mind, but also recognize Ben's stubbornness as a sign you need to do less pushing, more listening; people dig in hardest when they feel they aren't being heard.
"Reflective listening" (Google it) might help: "You're saying X," for example, or, "I hear you say Y." This whole situation screams for family therapy, though. Now that you're 26 and plainly feeling worn by the decade of extra responsibility, do look into it -- for you alone to start.
Bringing Ben wouldn't mean it is/was/ever will be your job to be Ben's "father." His relationship with his dad is independent of his with you; even if they reconcile, you don't get reassigned. You and Ben define and maintain your own relationship -- and allow it to evolve -- as it suits you best.
So you can just be Ben's brother because that's what you are. When Ben says you're the only "father" he needs, in fact, tell him how much you appreciate his saying that -- it is a lot of love and trust -- and also say plainly that you're his brother and always will be. Happily. Proudly. Make it a good thing.
Hope this helps, even a little. Check back in sometime?
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