Leonard loves Penny. It's a constant in The Big Bang Theory formula where the value of X is whatever Sheldon's obsessing about divided by a few racist or gross zingers that Chuck Lorre can't seem to help- he's like the Tourette syndrome of TV writers- and multiplied by the pure comedy genius of this show and the brilliant cast.

A while back, Penny and Leonard reached an understanding. His love would be the constant. The fact that he wants to marry her would never change. The variable would be Penny. He would never ask her again, she would have to ask him, but he would want all the bells and whistles.

That's not what he got. Last night, Penny finally got down on one knee and asked Leonard to marry her. But she was drunk, depressed about her career, and feeling that there was no life at the end of the rainbow.

Leonard feeling that this was a backhanded proposal of sorts, didn't say yes, but to his credit, didn't say no, unlike Penny who has told him NO dozens of times. Penny, to her credit, asked him to marry her when he pointed out that she hadn't wasted all her time in California because she had found him.

And she realized he was right.

Unfortunately, Leonard, after finally getting what he asked for, only to not have it presented with the love, devotion and romance he's always dreamed Penny would feel for him and finally show him, something she's always had trouble with, was a big letdown and he was not able to truly say yes. Leonard tries to explain what he feels to Penny, which sends Penny running from his apartment. Penny, in her drunken and forlorn state, only felt the sting of rejection in the one place where she's always had unconditional acceptance. (An aside: In a series where Penny solves a lot of problems with alcohol, it's notable that we've seen a lot of drunken Penny this season. Is this going to be "an issue"?)

Leonard has finally realized his self-worth: That he is every bit as much the prize at the bottom of life's cereal box for not only Penny, but any woman, if it comes to that. That the cost may be at the expense of losing someone who has truly been the love of his life is unbearably sad and even moves Sheldon to uncommon sympathy.

Chuck Lorre always finds a way, but how this is going to be resolved and keep the Penny/Leonard relationship alive is beyond me. It may be that the series is actually going to move past this relationship. (It has before.) Leonard and Penny have both dated other people for long swathes of time that left even the most devoted viewers feeling that they have moved on only to have some cosmic force - usually Leonard's love and Penny missing his devotion and friendship - throw them back together.

Penny has to change and evolve. Every character on this show has made progress in some way. Only Penny still has no last name (in a show where even Bernadette has two difficult-to-pronounce hyphenated names and even the comic book store guy is now a part of the regular cast with a given last name) and can still be found doing exactly what we found her doing in the very first episode: Working at the Cheesecake Factory and praying for a break in her acting career.

But some things can't be fixed. Some things, even in TV Land, can't be unsaid. Just like Leonard's self worth coming at a price, the evolution of Penny may at a very steep price- and break a lot of hearts in the process.

Notable Moments:

- Bernadette's nod to "When Harry Met Sally"

- The force of Keith Carradine being felt, sight unseen, in a phone call, even though he has only appeared once, several seasons back.

- Sheldon exploring the theory of comedy and dropping trou. Realizing that Sheldon's side experiments do not take the place of his serious pursuits - they are actually how he amuses himself and his more serious work does not suffer one whit.