Catra to Adora in ep 11: "Growing up in the Fright Zone wasn't all bad, was it?" Adora thinks Catra is questioning Adora's friendship, and reiterates that her defection had nothing to do with any sort of cracks or weakness in their friendship, it was entirely based on her inability to stomach the Horde's evil. But there's a second meaning to that line, because Catra is really the one questioning her friendship with Adora. Catra seemingly had some fun times with Adora, but Catra's life was mostly bad, and Adora was a tool to make life "less bad". Catra thought that was friendship.
Catra outgrew her need for Adora, but she was still clinging to Adora.
When they were kids, Catra picked a fight with a random superior enemy, and then Adora went out and threw down with that superior enemy with no hesitation, because any enemy of Catra is automatically Adora's enemy too (Adora seems to be doing this out of actual friendship, and not a selfish defense pact). But when Adora is blindsided by the Horde's evil and is forced to make an enemy of the Horde, Catra does not come to Adora's aid. Catra would rather beat Adora into submission and throw her to Shadow Weaver, for whatever miniscule rewards Catra might get for that. Catra doesn't love the Horde. She has no loyalty to them. At this point she still wasn't favored by Shadow Weaver or Hordak. She has no lingering attachments to leave behind. She just refuses to move to accommodate Adora's obvious need.
It's because Catra is outgrowing her need for Adora. The Catra/Adora dynamic has changed/is changing. Catra isn't afraid of Shadow Weaver anymore, nor anyone else. Adora's need to run from the Horde comes at the cost of another inconvenience to Catra, on top of the prices that Catra feels that she regularly needs to pay for Adora's friendship/alliance.
Catra was initially confused by her newfound separation from Adora (actually initiated by Catra, despite Adora's technical defection), but later she released Adora from capture, not because of their residual friendship, but because she wanted Adora gone. Catra likes who she's become in Adora's absence, and doesn't want Adora slipping back into her life.
The magic castle showed Catra these things, and showed Catra who she really was. When the spider grabbed Catra, she briefly tried to call out for Adora again, until she realized that she was capable of freeing herself. And then Adora runs in to try and save Catra, but Catra is disgusted by Adora's attempt to help, and the implication that Catra is someone who needs help.
Which results in Catra grinning like a sociopath as she drops a freaking-out and begging/apologizing Adora off a cliff, before making her move against Shadow Weaver, and having a totally contented look on her face as she watches the world burn. And then she finds out that Adora is still alive, and she says she's glad, because it means she hasn't lost the opportunity to kill Adora with her own two hands (she says while sadistically taunting Adora with the idea of torturing her new friends).
Adora wasn't a bad friend and she never betrayed Catra. She said or did nothing that demanded an apology, but she offered apologies regardless, and asked what she could do to try and preserve their friendship. Catra's the one with issues here, not Adora, and if Catra actually does have some genuine love or affection for Adora, it's buried so deep as to be unrecognizable. One could probably make a better case for Shadow Weaver loving Adora.