It doesn't necessarily mean "I'm in love with you" or "I lust for you", though those things may be true as well.

It definitely doesn't mean "I need you" or imply any responsibility on your part.

It does mean that I care about you deeply, that I'm glad that you're in my life, and I want to make sure you know it.

(Another entry that seemed like it would be a lot longer than it is.)