What's Your Definition of True Love?

With Valentine's Day coming up, I clicked over to a blog that was talking about love. Their definition of true love was "making the other person happy no matter what the cost." 
I've really been thinking a lot about that statement. I don't want to say the other person's definition is wrong, but in my heart, I don't think you can "make" another person happy. You can care about their happiness. You can do things that would bring them happiness. But you can't make them be happy. 
I have also been contemplating the phrase "no matter what the cost." Is there a limit to what I will do to show my husband I love him? If there is, does that mean it's not true love? For me, I think there are boundaries and if it is true love, your significant other won't ask you to cross them. 
What do you think? What's your definition of true love?