The Netziv suggests that the command of “lech lecha” forced Avraham to stay away. It wasn’t until after the akeidah, until Avraham passed this final test and reached the pinnacle of tzidkus, that he was able to re-establish his relationship with Nachor and family.
Perhaps this is not just a technical din – the issur of “lech lecha” needed the matir of the akeidah – but rather is a psychological truth. It’s sometimes easier to deal with strangers than to deal with one’s own. While others saw greatness in Avraham, his family back home, whose recollection of Avraham may have been colored by their memory of little “Avi” in diapers, may not have been able to see him in quite that same way. Perhaps Avraham’s family in Charan would and could push his buttons and influence him in ways that outsiders could not, creating enormous difficulties. There are plenty of real world example of people who are called “HaRav haGaon” and accorded tremendous respect by outsiders, but whose words don't carry the same weight by those who can simply call them Aba/Tatte/Dad. This is the way of the world. Avraham faced the same difficulty (albeit with further removed family). The fact that it was only after he passed the akeidah that he was able to go back shows just how difficult this challenge is.
2) Rashi explains that the purpose of this long list of children born to Avraham's family is to introduce us to Rivka, the future bride of Yitzchak. The akeidah brought Avraham to the stark realization that had Yitzchak been killed, he would have been left with no lineage to carry on his message --Yitzchak was unmarried and had no children of his own, and therefore Avraham had no grandchildren either.
The Shem m'Shmuel asks: what's the point of looking back at what might have been? There was not going to be another command to do an akeidah -- the test was over and we know Yitzchak's life was never really in danger. It sounds like Avraham was moved by regret over not having married off Yitzchak earlier to have grandchildren, but post-akeidah the point was moot.
The Shem m'Shmuel reads Rashi as follows: Avraham thought to himself that it was the promise that he would be blessed with descendents that prevented the akeidah from actually taking place. Had Yitzchak been married and had he had children, meaning, had there been descendents to carry on Avraham's legacy, then Hashem would not have had a reason to stop the akeidah from actually being completed b'poel. This was Avraham's regret -- that his choice to not marry off Yitzchak caused the akeidah to be stopped short.
If it was anyone else, they would have been breathing a sigh of relief and dancing with joy at having been spared completing such an enormous test. Avraham Avinu, however, so desired to carry out Hashem's will that he was filled with regret thinking that something he had done caused the test to be aborted before being fully completed.