There actually are vague indications of the reason why Elliot doesn't like getting introspective in the archives, but what are they? HA! As though I'd reference link the appropriate comics prior to Elliot actually getting introspective, and that could takes weeks! Months! YEARS!

Or tomorrow. You know, whenever.

And now for alternative comic dialogue theater:

Ellen - "What look? This shocked look in response to saying you felt like you were cheating on Susan at times? I wasn't reaching any sort of conclusions about what sort of feelings you may or may not have for her. I was thinking about that other thing. From before. That's not related. Let's talk about that again."

Elliot - "I totally believe you."