Cohabitation Agreements: Is There a Legal Maximum Length to an Engagement

My question involves marriage law for the State of: California

I've been engaged for 3 years to my girlfriend of 7 years. Recently she's heard from a law school student acquaintance of ours that she can legally force me to "shit or get off the pot" because contract law says there is an implied duty of good faith and fair dealings that's enforceable in court. Making an offer to marry without any intent of following through in a reasonable time frame is not good faith otherwise known as fraud or constructive fraud. Statistically there's 4% of couples who takes longer than 1 year from proposal to marriage so 3 years is not a reasonable time frame. If I refuse to marry and we break up, my fiance can sue me for damages for whatever decision she made based upon my proposal.

Is our law school student acquaintance right ? It sounds like a bunch of crap to me. I should be able to take whatever time I need to ready myself for the wedding. Can't find any precedence or similar case through google.

Cohabitation Agreements: Is There a Legal Maximum Length to an Engagement