The OP is afraid she's going to get a sexually transmitted disease from a "forgotten" condom?
And, yes, the mystery man is a jerk. On the other hand, maybe he's still checking himself over to see where the condom went.
Any sexually active woman who relies on condoms owes it to herself to make sure it's on both... at the very beginning and the very end.
Now that the condom was left behind, what about pregnancy? Doesn't seem that the condom is effective when it's "off.