it's just he didn't see past his own pain to even consider that Martha was in love with him.

While I generally agree with you, I don't think this is totally right. I think, at some point he realised that Martha had thing for him, but decided to ignore it. Probably because he hoped it'd straighten itself out and because he was desperate not to be alone, without a friend/companion.

The whole thing was just unfortunate but it happens all the time. People being hopeful or better said delusional that another person's feelings towards them will change in a way that is favourable to them and therefore sticking with something longer than is healthy.

It's just one of those things...