This is all Castiel's minor relationships he encounters through his life and time on earth. Though by Season 6, Castiel has severed most of his relationships, presumbly as a result of his quest to stop the civil war raging in Heaven. Now that he has become God for a short time, it is not known if Castiel's former relationships have been damaged beyond repair due to his actions or if there's any hope of fixing them.
Zachariah is described as Castiel's superior, in other words his teacher, and thus is forced to respect him, holding the utmost respect. However, after Castiel is resurrected the first time, this respect goes away and Castiel stands up to him and scares him off to save Sam and Dean. He later aids Sam and Dean in rescuing Adam Milligan from Zachariah, only worried about the fact that he will be unable to defeat the more-powerful Zachariah and five other angels, but coming up with a way around that. Castiel essentialy sacrifices his powers to give Sam and Dean a shot at Zachariah, allowing Dean to finally kill him.
Although, Balthazar did help Castiel and aided him in the civil war in heaven, Balthazar was now under Castiel's command.
However, after learning that Balthazar betrayed him and gave away his location to Sam and Dean, Castiel, knowing that his former friend had become a loose end lured Balthazar to a place under the guise of talks before sneaking up behind the other angel and hitting him in the chest with an angel sword. This resulted in Balthazar's death and it's presumed that Castiel felt some guilt over killing his former friend.
Although Uriel went rogue and tried to convert Castiel to his own plan of helping Lucifer destory mankind. Castiel refused and the two sworn rivals then engaged in a bitter fight to the death. However just when it looked Castiel was going to die, former angel Anna Milton came up and stabbed Uriel, killing the older angel and saving Castiel's life.
Purgatory. Castiel needed the souls to win the war, so he secretly began working with Crowley. He even went so far as faking Crowley's death.
Castiel did help collect creatures for Crowley. Eventually, Castiel betrayed Crowley and opened the door himself. Thus their working relationship was nullified as a result of this. Castiel later re-emerged, declaring himself the new God and killed Raphael before deciding to spare Crowley, saying that he has plans for him. When Crowley reunited with the now-insane Castiel, he was furious that Castiel was still alive and that the Winchesters were harboring him as Castiel had tried to enslave him. However, realizing that Castiel was insane, Crowley left him alone for the time being, stating that it would be no fun to kill him in his crazy state where he refused to fight and asking for Sam and Dean to call him when Castiel regained his sanity so they could fight. However, Crowley respected Castiel's wishes for him not to harm Meg at the same time as the Winchesters needed Castiel and Castiel was fond of Meg, though he later captured her once she was out of Castiel's sight. It is unclear if Castiel is aware of this. When Castiel returned from Purgatory, he faced off with Crowley even in his weakened state. Castiel tried to smite Crowley, terrifying the King of Hell into fleeing. Castiel managed to damage Crowley's current plans at the same time by breaking The Word of God in half, causing Crowley to only get away with one half. Crowley later captures Castiel and shoots him in the gut with a gun loaded with bullets made from a melted-down Angel Blade, severely injuring him. Crowley is able to correctly deduce that Castiel has the angel tablet inside of him and painfully removes it from him. In his weakened state, Castiel is unable to do anything, but manages to escape when Crowley is gone.
God, but follows his orders out of faith. He was obedient until Dean began putting doubts in his head. Castiel eventually rebels against heaven (and God) and helps Dean. In Season 5, he begins to look for God in order to stop Lucifer using Dean's Amulet, but is let down when he finds out that God doesn't care.
Unlike any angel, Castiel has been brought back by God, twice. As an apparent reward for his role in averting The Apocalypse, God increases Castiel's power and upgrades him to seraphim. Later on Castiel asks for God's help, but God doesn't respond. Following that, Castiel later proclaims himself to be the new God, thus severing their connection and possibly becoming the greatest threat that the world has ever known. Despite this, God apparently resurrects Castiel for a third time after he dies due to being possessed by the Leviathans. Although God brings him back with his powers intact, he has no memories for some reason, though they are apparently just buried and he is able to eventually regain them by vanquishing demons. However, Castiel now believes that this and his other resurrections were a punishment that gets worse each time and that if he dies again, God will bring him back again to continue this punishment.
Anna's relationship goes back thousands of years. They served together in heaven in the same Garrison. They were probaly close as Castiel states "we have history together". After Anna falls, Castiel and Uriel are the ones who are asigned to bring her in. Castiel says he is sorry but he will kill her because orders are orders. However, Anna gains her grace back and escapes. The next time he sees her he tells her he has orders to destroy her, but she knows that he won't. She calls him by his nickname Cas and questions whether what he is doing is right. She wants to work together with him but he becomes angry and states that he is nothing like her, and tells her to leave. Later, he calls her back and asks her for help on what he should do. She tells him its time for him to start thinking for himself. Anna later saves his life during the fight with Uriel and kills Uriel to save Castiel. When Anna confronts him about letting Sam out of the Panic Room he betrays her trust and has two angels take her away. She eventually escapes and is angry at Castiel for turning her in. She wants to kill Sam but Castiel tells her that if she tries he will kill her, despite what they have been through together. This is the last time they see each other before Anna is killed by Michael.
Ever since Raphael killed Castiel in Lucifer Rising, the two have been enemies. Before Castiel rebelled, it is believed Castiel probably respected Raphael due to rank. Although after being killed, Castiel returns and confronts Raphael on where God is. Their hatred for one another escalates when Raphael wants to restart the Apocalypse. Castiel refuses to let this happen and with a deal with Crowley, he starts a civil war in Heaven. After absorbing the souls of Purgatory, Castiel kills Raphael in a similar matter himself was killed in.
Heaven, he is being trapped in a circle of Holy Oil by Lucifer who tries to persuade Castiel to work with him by listing things they have got in "common". He also makes it appear as if he is the victim and that his only mistake is loving god too much. Nevertheless Castiel does not fall for that so he leaves Castiel in the circle while Meg stayes with him to watch out that he does not manage to free himself.
Castiel and Bobby- Castiel and Bobby's Relationship over the years.
Meg and Castiel - Castiel and Meg's Relationship over the years.
Castiel and Sam - Castiel and Sam's Relationship over the years.
Dean and Castiel - Castiel and Dean's Relationship over the years.