but maybe now Marten is just thinking "Ya know what screw this, I am going to work on myself and worry about myself for once"
...suggests that he can satisfactorily take advantage of the situation.
And to be frank, Marten was crazy about Faye at first and he took that rejection remarkably well. You say he's not a saint, but he's been portrayed as such throughout most if not all of this comic. He is 'The Good Guy'.
And you know what? Even good guys have their limits. Additionally, the situations with Faye and Dora are very different.
1.) Faye moving in to The Talk was three, maybe five months at most. Dora and Marten have been going out for at least a year.
2.) Faye was a friend/roommate/hopeful girlfriend that transitioned into a friend/roommate. Dora was a long-term girlfriend who looks to transition into an at-best friend/awkward-to-be-around ex.
3.) Faye's rejection came in a calm collected manner with a valid explanation of deeper issues after months of mixed signals. Dora's rejection comes in the sound and fury of a fight with no explanation of deeper issues after a year of what seemed to be a mostly good relationship.
4,) Faye said, "I want to fix my issues". Dora, from what we've seen pending further recounting of any post-1799 conversation, said, "I can't fix my issues.
I give up."
These are markedly different scenarios here.
True, Marten may not be acting
exactly in character here. But getting dumped hard is the kind of stressing situation that makes people act not in character. That said, he's having a very human reaction. Anger's been building up for months even though he told himself he could fix it. That's just the noble creature that he is. But he's finally burst. He's bitter. He resents having to put up with Dora's crazy when she doesn't seem to be doing a thing to fix it. Maybe for once he's being actually selfish and saying that he doesn't need her insecurities if she's not going to work through them with him.
Good guys like to fight the good fight. But sometimes even they realize that something isn't worth fighting for. They won't like it. They'll still want to fight for happiness and good. But some battles are just un-winnable.