Phoebe left Cole because of her guilt over the fact that she CHOSE evil, while he was possessed.
I feel like the whole nasty desperate Cole arc started when Phoebe basically chose to go along with plans and Cole was under the influence of the source.
I don’t feel like it’s THAT outrageous that Cole asked Phoebe to use the Grimoire to bring him back. If she didn’t want to, then find another way, hell CREATE ONE. He wasn’t even really dead, rather he was displaced.
Phoebe actively despised Cole because he actually represented the good that was clawing to get her attention, screaming for her to save him. Her ultimate failure bc what did she do? Lean into the temptation. Betray her blood. Revel in the pain of others.
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I love Phoebe really I do but I just really feel like she pushed Cole away bc she chose evil and was trying to pass the guilt.