This is such dicey territory that my advice would be: Unless you and your ex broke up on really good mutual terms that just came from not really working as a couple, but you're still friends, and friendly enough to have a really open conversation about this subject, you should just abort the project.
I'll give a bit of leeway IF and only IF the character was only vaguely based on or inspired by them and doesn't obviously share the same likeness or name (AND that includes if their name is that person's common online handle) and you haven't made it public in a lot of comments etc that the character is based on them.
I cannot even imagine having some ex using my image and name in a comic after we'd broken up. I despise other people putting words into my mouth that I never said, so the idea of letting somebody who may hate me control my image is absolutely ghastly to me.
Let's imagine a scenario where:
Comic artist is actually an absolute slimeball and really abusive to victim, they openly flirt with other people but gaslight their partner if they ever bring it up, they try to coerce their partner into sex when they don't want it, they are controlling and manipulative... but all the while, they're drawing a comic which depicts their relationship with the victim as lovely relationship goals funtimes! After getting some support from friends and family, victim musters up the courage to leave Comic Artist.
Comic Artist continues to depict the relationship as being a thing in their comic and being yay cute happy couple! Victim keeps having people talking like they're still in a relationship and saying "wow, I wish I had what you have with comic artist, they seem so sweet and good to you!" which unsurprisingly pisses off victim after what they've been through and what the relationship was really like.
Victim, who is much less well known and widely publicised than comic artist says "Comic Artist, please stop using my image in this comic. It's not an accurate depiction of our relationship and I didn't give you permission". Comic Artist, who effectively has control of victim's public image here, makes a huge public fuss of how victim broke up with them and they're so sad about it and oh, woe! "The comic may have to be cancelled because victim left me and I don't know whyyyyyy!" This basically galvanises the comic's fanbase of several thousand people against victim, who, reminder, has done nothing wrong here, and they start getting death threats and abuse for destroying the comic they love, and for destroying that beautiful perfect relationship (because everything the fans know about it comes from the comic, and the comic depicts comic artist as maybe kinda dorky and childish, but well-meaning and sweet).
Meanwhile comic artist gets loads of support, "don't end the comic just because of this" "Just make that character turn out to have been evil" "Kill that character off!" ...Hey! Lightbulb! What a great idea!
Comic artist writes an arc to write the victim out of the comic in which they turn evil, go on a murderous rampage and die a gory death getting eaten by rats or something, their last words are "I'm sorry... You deserved better" as the virtuous hero sheds a single tear, then they get a new hot partner. The fanbase are like "YEEEAH! Serves them right!"
So after all the emotional abuse they went through, the victim then has to endure seeing themselves depicted as a twisted and evil strawman propping up the comic artist's total lack of guilt and dying a gory death, and knowing that for thousands of people, that's how they will be thought of; as a villain who deserved to be eaten by rats.
Do you see how awful the power imbalance and abuse of power is in that story? When viewed from the victim's perspective, it's really just awful. But this isn't a completely out of the question scenario. Many elements of the story are based on things I've heard of or seen happening in couples where one person has far greater notoriety or popularity as a creator than the other. Sure, it's nice to imagine that in a breakup scenario, the comic artist is the poor underdog abused nerd getting their own back on the abusive and more popular partner in the only way they can... but what about when it's actually the other way around? When the comic artist was abusive and continues to control the narrative in the eyes of the public?