Wait I just had a weird idea HERE ME OUT; maybe what causes the emotional decay between the two is because;
back then 073 was more like 076 in the future, more brash and harsh, with snarky remarks. 076 was more like 073 in the future kind and loving, following Cain like a lost puppy possibly gullible. As kid they probably were pretty close for a long time to at least develop a strong connection (maybe love? Or something close to develop something deep.)
What split them up was not the offering of God resulting in Cain getting jealous and bonking Able on the head with a rock.
But instead, in Cain's wandering, him growing wiser and calming down. He realized that he genuinely fell for the person he killed. In this, he grieve in what could of been.
Abel being to kind. He made a deal with an entity that sell his feeling maybe his soul to come back. He didn't understand why Cain did this but held hope.
He came back But that wasn't Able, When they both meet in the past, Cain in guilt could never see this "Abel" as his brother. instead a cruel mockery of what ones was, Abel couldnt understand, didn't you still love me? He would ask. Cain would shake his head and respond, you are not my brother, not anymore.
Cain in fear of tarnishing his little brother memory. Ran like a coward. while Abel in desperation cried out to him to come back.
This is what broke Able, I thought you loved me, you promised, in his (076) mind he hasn't changed. While young he fell for the Cain and and still was. But after that final betrayal. The emotional turmoil. It was to much. He grew twisted, bitter, that love was still there but more sickening and volatile. That love turn into a rage that's finally at its tipping point. He grew to love Cain, now as his murder.
In Abel, this turned into an obsession, to seek Cain out to force him to love ANSWER for what he has become. In Cain, to never interact with this Able again, selfishly want to stay in the past.
IM SO SORRY FOR THE LATE ANSWER I DID NOT OPEN THIS BLOG IN A BIT
this is sogood btw, delectable, i might take some things from this idea actually