Cancelling the first date after developing an ick?

Made dinner plans with a guy (28M) I?ve (22F) been talking to. He was very consistent in communicating at first (FaceTimes, long phone calls, would at least text me to see how my day was) then went entirely radio silent once we agreed to go out this weekend (he?s back in town) - plans were made two weeks ago and it?s been like this since.
Normally this wouldn?t bother me, however, he always acknowledges his decline as ?being busy?. However, whenever I check my Instagram, he is actively posting or watching what I share. Both of these are red flags, one being the hot and suddenly cold communication, and the other being how often he is on social media. I suddenly can barely get a text back because he?s ?busy? ? AKA on social media what seems like every hour of the day.
Not what I?m looking for in someone I?m dating, nor do I want to try to change someone.
I?ve grown exhausted from dating inconsistent men. I no longer want to entertain going out with him if this is what it?s like before we?ve even had a date. Been there done that and it usually ends the same way.
What would be the best way to cancel the date and acknowledge that Im not interested anymore?
TLDR; after noticing two red flags, I am not longer interested in going out on a date with a guy I?ve been ?talking? to for weeks, but am not sure how to nicely address it.


Source.