Why was Marlene so mean to Joel at the end?

I just beat it again and reviewing the end, I just don’t get it. Their interaction was so tense and unkind despite the fact that Joel lost Tess and brought Ellie all the way, she could’ve been a lot nicer and that likely wouldn’t have changed anything but seems a bit more humane. Not to mention, doesn’t she still owe him for a guns payment?