Status: Family, Twin Brothers; Close relationship restored, Currently Allies, Former Enemies. Love each other, Care about each other.
Gabriel and Michael are the twin archangel brothers, born together and stayed together for eons. They share a deep psychic bond that allows them to communicate telepathically; they completed each other, yin and yang. Gabriel described Michael as his "better half."
However, both of them had several goals over many millennium. They still love each other, but are on opposing currently because of each of their side in the Extermination War. Gabriel sought to end humanity, but Michael planned to save it.
At the beginning of season 2, they are both still at odds with each other. However, when Gabriel sends one of his angels to see if Uriel survived the explosion, he is devastated to learn that she didn't. Gabriel tells news about Uriel's death to Michael and Michael reacts by violently beating him. Gabriel lets him being its Michael's way of showing he's upset. In the end, they decide to work together to retrieve Alex Lannon out of New Delphi. However, both stay behind when Noma and Alex escape. Noma was critically injured and now, Michael and Gabriel bond in a strange way while being tortured by Julian. Gabriel then comes to realize that Michael's beliefs are just as important as his own, so he sacrifices himself to stay in New Delphi. He lets Michael go help Alex Lannon. After being tortured by the Amphora by Julian, Gabriel now has the intense hatred to kill his brother, Michael. Motivated by this false hatred, Gabriel releases the Amphora onto Vega in an attempt to hurt Michael and his allies/friends. However, Gabriel plans to hurt Michael before he actually plans to kill Michael. Michael does not know he is the one behind this and doesn't know that he is infected with the darkness, yet.
Near the end of season 2, Gabriel, corrupted by the darkness of the Amphora, defeats Michael who reveals to him that he believes Lucifer is alive and using the town of Mallory to come back. Gabriel drags him to Mallory where the Prophet confirms that Michael is right. Gabriel collapses from the effects of the darkness, but Michael is able to get Lucifer to heal him in repayment for Michael not destroying his body. Gabriel apologizes for his actions to Michael and flies off with him when they realize Alex is with Noma and thus in danger. They are currently on the same side again, after years of argument between war and what they believe in.
Being the series was cancelled, it can be assumed that Michael monitored Gabriel's quarrels with Alex after they saved the Chosen One from Noma Banks and being delivered to the devil himself. Both archangel brothers, along with Alex, possibly worked together to eventually defeat Lucifer and his followers.