If you remember, Andy asked everyone with a show of hands, who would work with Mat again. All of them raised their hand with the exception of Sandy. When Andy pointed that out, Sandy said she liked and needed reliability. Mat, being who he is, got his feelings hurt and his reaction was to go at her like a petulant child, rather than be an adult and realize why she said what she said. From that moment on, he had no use for her. Sandy even told him that he didn't know when to stop talking and that his problem is himself.
I liked this crew for the most part with the exception of Mat and Lexi. It was refeshing to see that most of them were supportive of each other, helped each other out and got along. IMO their drinking didn't come close to some of the antics of other past crews.
I do think Katie should have kept Delaney, if for nothing else than laundry as others have said. However, it seems Katie had very strong feelings that Delaney had lied on her CV and she couldn't get over that.
Overall I didn't care for the reunion. Because of the format, they were all talking over each other. They were laughing but didn't seem to have a whole lot to say most of the time. Courtney looked absolutely out of it. At one point she appeared to be on the verge of passing out. That was ridiculous.