Saying "You Better" as a response to I love you

Need more context

Flippant response. Not the one you wanted to hear, huh?

Or, it's a song.

It's an idiomatic sentence. It's an incomplete sentence that the intended target is to fill in the remaining words in his or her mind.

I said to a man "I love you...you know"

He responded "You better (love me)."

Love me is implied in his incomplete sentence. He could be saying it jokingly (hopefully) or aggressively (like a psychopath's choice of phrasing). You don't provide enough info for us to guess the speaker's motivation and intention behind his words.

It could be an order.

Or it could be a playful : "(I love) you better"

or just silly -- you better! <wink>

I did mention he could be joking in my post.

I too took either as playful or a threat, hard to tell from here.

How was the tone, facial expressions, etc? There is so much more involved in communication than just the words. It could mean anything from an insult to being funny, to lack of confidence, to desperation, to being embarrassed.

You really need to provide tone, and other background for us to determine. It could simply mean that this person feels the same way, but lacks confidence to come right out and say it - so makes it almost into a joke. Or the opposite they have no desire for you, but didn't want to hurt you so made it into a joke.

Or it wasn't a joke at all - but was so desperately in love with you that fit their response (in that you better or it would just kill me if you didn't love me).

Don't worry. It's good!

When I say I love you he said I know...
I always laugh because our conversations
Are always lighthearted fun.
Once I said how do you KNOW?
And he said because I believe your every word.
I was satisfied. And love him even more. Lol

So good luck!