Think about it. Roman is supposed to be "good" creativity, versus Remus being "bad" creativity. He holds himself to a massively high standard because of this, forcing himself to sacrifice his own needs and desires because he believes it's the "noble" or "right" thing to do. And he does this specifically to separate himself from Remus. He even states in DWIT, "It's kind of like looking into a fun house mirror... except you see everything that you don't want to be." He does everything he can to be this perfect, good side for Thomas, even if it means giving up his own very purpose. So when Janus compares him to Remus, it's a really, really tough blow- mostly because Roman sees it too. All he wants is to protect Thomas and live up to his expectations, and he projects his own internal battle between his true desires and his need to be good onto Janus (gosh it feels weird using his real name). AND AND when Roman mentioned all of this being his fault, of course Thomas and Patton addressed it, but it was dismissed fairly quickly and he probably continued to blame himself, continuing this internal war within him. If Roman didn't feel this pressure to separate himself from any and all things "evil," then he probably wouldn't have lashed out or said any of the rude things he said to Janus at all. That of course doesn't justify him being mean, obviously, but in the very least it makes sense (at least it does to me). In the end, Roman is more than just insecure at this point and it shows. He hates himself and he's tearing himself down in his attempt to help Thomas, all to discover that he's really just hurting him more. He's putting Thomas and everyone else before himself.
IN CONCLUSION I LOVE ROMAN SANDERS AND HE DESERVES ALL THE LOVE IN THE WORLD THANK YOU FOR COMING TO MY TED TALK.