I really do think that Marten is doing enough to show her that he likes her and isn't just in it for the sex. It's natural for him to not be trying to LOOK for hints or signs, though, since he has set his mind on the "she's leaving, this is just a fling" mode. He's doing this so HE won't be hurt-- and probably because that's what he thinks she wants. If you know (or think you know) that someone is only ever going to look at you as a fling or someone to have fun with for a short period of time, you are going to go out of your way to NOT see any hints that they may actually like you or want more from the relationship. If you get your hopes up, you could a) be hurt and b) lose what little connection you do have to the person.
Plus, Padma has presented herself to him as someone who speaks/acts first and thinks later. I'm sure he assumed that if she wanted more or was unhappy with something that she would have SAID it. She didn't seem like the type of person who would just run off and disappear on the person. If I were Marten, I would be completely confused at this point. Sometimes he does silly things, but I don't think he has done anything "wrong" in this situation.
And if he tells her that he loves her at this point, I'm going to...take a deep, calming breath. Too soon for that.