I think regardless of what drug(s) he may have been using, he was a bad investment of your time all the way around.
There is no one behavioral thing that would tell you if he's on coke. There are a lot of signs that point to drug use in general - but no one here could point to just one behavior.
I hope that in the future you'll get out at the first signs of someone taking advantage of you and/or being involved with other women. Life is difficult enough without that.
Trust your own intuition.