I think the crux of the matter simply was, both Dora and Marten had issues, which they've ignored since we, the readers, first read the comics. By ignoring these issues, they were allowed to fester, and spread and infect. I mean, look at when we first met Marten (and I will be sticking with him for this example), he's lonely, depressed, hates his job and just doesn't have the willpower to actually try to change his life or to even talk to a woman in a bar.
It actually takes Faye to come up to him and say hi before we see any slight change in him, but it doesn't take.
It actually takes Dora to kiss him to make him realise that there was a girl right in front of him who actually wanted him. But it doesn't take.
It actually takes encouragement from his mother and Dora to consider quitting his dead end job, but of course, he was fired so he couldn't assert himself that way. And which leads him into a job which from all reasoning is perhaps even more tedious than his office job.
The majority of the major events in Marten's life have been enabled by other people or outside forces, which means Marten never learned anything for himself, how to stand up for himself, to go after what he wants. Even now, when the best thing that happened to him dumps him, his only reaction is the same default one that he has used since day one...retreating into himself. We see no postivie growth now, only growing anger, which, yes, it can be useful can also be far more dangerous than apathy.
Marten might have grown a pair of balls but it could also be the match thrown towards the powder keg. Which in a way, is a great tribute to Jeph's skills as a writer that there is the potential for such a Milquetoast character to transform into a seething mass of bitterness.
Both Marten and Dora need to recognise this now or things will get far worse.
And yes, I am one of those people who believes Marten should head home to California for a time, both to think things through and to get away from the sympathy and awkwardness that is bound to arise amongst the cast now.