I would certainly tell the shadchan why you are hesitant to continue. The boy may not realize how he is behaving and coming across. Certainly the issue of talking about past dates should be mentioned. He should know that, even if you say yes to another date, if this continues, then you will say no after the next date.
But, I would do this keeping in mind that he might put on an act after this and it may be harder to see his true self at that point. It is not easy to be married to a person who is constantly looking at the negatives of situations.