Warning! Spoilers for Avengers #54 by Marvel Comics
The bad blood between Black Panther and Namor the Sub-Mariner is still apparent, as the hero just confirmed he hates his fellow Avenger more than any other member. In Avengers #54, Black Panther admits to Namor they could use all the help they could get against the Multiversal Masters of Evil, but that doesn't mean he still doesn't hate him now that they're working together.
T'Challa has understandably viewed Namor and Atlantis as a threat and enemy of Wakanda, even while cautiously working alongside the hero. His fears came to fruition during the Avengers vs. X-Men crossover event, where Namor invaded and flooded Wakanda in an act of war after Black Panther welcomed the X-Men protection in his kingdom. The Sub-Mariner's actions killed countless Wakandans, leading Shuri (in New Avengers) to lead an attack that would leave numerous Atlanteans dead. Furthermore, Namor would escalate the conflict by leading Thanos directly to Wakanda, in an event that ended with Namor being kicked out of the Illuminati for his betrayal.
In Avengers #54 by Jason Aaron, Juan Frigeri, David Curiel, and VC's Cory Petit, Earth's Mightiest Heroes reel from an attack on their Celestial base by the Multiversal Masters of Evil. Namor tells Captain America he will not sleep among his fellow Avengers and only rise from the depths of the ocean when needed. His response causes Captain America to snap, as he calls him out his destructive actions and tells him he's in Avengers custody and will obey their rules. Namor accepts the conditions and jokes with Black Panther that he thought he'd be the one who would need convincing about joining the team. Black Panther responds by telling Namor he still hates him.
Black Panther doesn't mince his words, telling Namor he still hates him for what he did, revealing to his fellow Avengers he despises him "far more than [Captain America] ever will." However, T'Challa realizes the threat they're facing and understands they'll need all the help they can get, even if it comes from Namor.
The moment between T'Challa and Namor illustrates why Black Panther is one of the leaders of the Avengers and a great hero. Despite Namor the Sub-Mariner being responsible for some of the most tragic moments in his life, T'Challa is willing to put their past aside temporarily as they face a more significant threat together. But that doesn't mean he will suddenly not hate the hero anymore. On the contrary, Black Panther isn't willing to forgive and forget what Namor did - he's just not acting on his hatred given the gravity of the situation. Avengers #54 by Marvel Comics is in stores now.