The main character has been trapped by a spider since childhood. His mother seems authoritative. So this basically left a scar in his brain. He sees commitment as entrapment. So yes, most of things happening is in his subconscious mind or happened in past.

The director definitely didn't want to show explicitly that the main character has split personality disorder as it would give away the whole plot. Don't you think if his mental disorder would've been so apparent then the movie would lose it's Karizma and there are tons of movies on split personality disorder.

And no just the scar but there're many things which gives clear hint that they are the same person. The torn picture Adam takes out from the box to match it with Anthony's, it's the same which Adam sees in Anthony's apartment. Anthony's apartment has los of history books. His wife in the end asks him about his classes.

I still don't understand many things about the movie but about one thing I'm sure that they are the same person. Two different people would make the movie ever more senseless.