The thing is, repetition isn't necessarily a bad thing, here. We all have traits, and we tend to repeat our mistakes a few times before we really learn from them (if at all). Just as Faye has yet overcome her dependence on alcohol, Marten has yet to overcome his tendency to put her well-being ahead of everyone else's, including the lady he's actually in a relationship with. I'd argue that it would be worse writing, almost bordering on bad fanfiction, if he magically got over that trait and was the perfect boyfriend to Claire. It's way too soon to be talking a break up for those two, but as far as presenting itself as a speed bump in the relationship, it's logical and consistent with Marten's past behaviour.
Incidentally, I think that's all it is, just a speed bump. If anything, the issue resurfacing provides an opportunity for character development, for Marten to be aware of what he's doing here. Perhaps it might even give him greater perspective on what happened with Dora. Not that Dora doesn't share responsibility for that, her own issues caused...well, issues, but Marten's attachment to Faye was a factor too. And so, it remains to be seen if he learns his lesson in the long run.