@Gigi523,
I would say all responses here do seem reasonable. I will offer you my insight:
"We were supposed to see each other again, but he cancelled because he said that he had a terrible day and just wanted to be alone. That was on Thursday and I haven't heard from him since. "
This is funny, but this is what happens to me when I have terrible day, what is pretty normal life occurrence I believe. If you are tired, stressed, something got into your way, maybe you don't want to see your new partner for it might end up in trouble. For instance (very likely to happen!) you will look intimidated, irritated, tired, uninterested and your partner will be asking "what is going on, is is loosing interest ot what?" Simply spoken, at the beginning people want to show the good side of them and if they are not in a mood, they might reconsider postponing meeting for later.
It has been 4 days, I would say quite a long time, so maybe smt. serious is going on.
My advice: non-obtrusively ask what is going on. You can't loose anything by that. either he responses or not. If yes, there is a chance to chat it out.
And btw. "I don't want to waste my time on him" - how old are you exactly and what do you do? Are you in a hurry for marriage or are you CEO of large corporation that your time is so precious you can't afford to wait one or two weeks to figure out what is going on? You let him shag you twice, yet you wont tolerate week of cloudiness. That is not a very good attitude.