What does "let off" mean in this sentence?
- I wasn't sure I'd see you after your freak-out at the investment party...
- Freak-out? I let you off easy.
- One minute I'm under the impression we might actually have a future together,
and the next I catch you lip-locked with Nolan Ross

Question

Answer

http://dictionary.cambridge.org/dictionary/learner-english/let-sb-off

Answer

The conversation doesn't make sense to me. Who is talking?

Answer

It means to not give someone the punishment they deserve from you or another.  
A related phrase is "let somebody off the hook."  The analogy there is to a fisherman, who has caught a fish, but instead of eating it, he lets it back into the water.

Letting someone off the hook, then, is like that fisherman.  He has some power to punish or harm a person as a result of their actions, but he can "let them off the hook" and pretend it never happened.