I don't think it was selfish on his part. After all the sacrifices he made, he deserved a life to rest and be with the love of his life. I think he did try his best to move on, but there are just some things you can't ever completely let go, which for him was Peggy. I am a big believer that he was always Peggy's husband and father to her kids. I agree with the writers because a.) they have written all of his story from the beginning while the directors are the ones mainly responsible for putting it on the screen. The writers are the authors of his story. They also created Agent Carter so I think their opinions mean more than the directors, plus the directors are always contradicting themselves. They don't even have all the answers to the movies and have been stumped multiple times by fan questions. One perfect example was one question a fan asked about Bucky and Zola from Winter Soldier and they could not answer it.
So if we go with that he was in the prime timeline the whole time, even if he could have done something about Hydra, time would have corrected itself. Remember Tony's endgame line, "when you mess with time, it tends to mess back." Also, the TVA would have put a stop to it as well to preserve the "sacred" timeline if things did not go as planned. If you believe he is an alternate universe, then he did help out when he needed to as that is what the directors have stated.
With his decision regarding Bucky and Sam, Bucky knew all his plans and did not stop him nor argue with him and agreed that Steve should be happy. Sam also said he was happy with him when he found out. Bucky and Sam will be just fine, plus how do we know Steve is not there now. Yes, they say he is gone, but where is he? They are being very ambiguous about his fate.