Sorry to disappoint, but this is no troll. Thing is thing, Marty is that guy.
Look at it from her point of view. A confident and comfortable stranger walks into her place. He's been through a break up recently, but he's no creep, he's good people. She's feeling despondent because she feels she is obligated to leave and, even though there is a guy there that she knows damned well is into her, she wants to have her last days in this place be memorable. She can't ask the big lug, cause she can't stay, she can't be what he wants her to be even if she wants to. She has obligations. Sure, she could find some creeper, like Steve, but she wants someone who is tender maybe. There he is, Marten. Right there. So, she asks him on a hike, a very personal thing, tells him she's leaving. All the subtext is present, "We ain't got much time hun, let's make memories," she says in not so many words.
Marten could see it for what it is and take her up on the offer. Spend the next few weeks making her feel like a queen with the earth at her feet and the clouds for a crown, kiss her goodbye at the airport and know they'd both live long happy lives remembering how fleeting yet perfect it was... but no.
The fans won't allow it. Marten has to be "that other guy." The one that we are all glad we aren't.
Pity, I could image him finally walking without a slouch after the airport trip, and all the other QC universe women thinking, "wow, did you get a haircut? you look great!"
If you don't get what I mean, you may someday, but likely you never will.