Saying 'thinking about her in a sexual way is wrong' may have moral value, but don't forget we are only human. Humans = animals, and animals = drive for reproduction. If you think about someone sexually, you're not lowering your value as a human, you're simply reacting the way nature intended. Now, if you ACT on those thoughts, then by all means, it is completely wrong, until the correct situation is acquired - marriage. Now, thinking about her in a sexual way is a LONG SHOT from kissing, and kissing is just another way of expressing affection. In what way is kissing more important than hugging or snuggling (if snuggling be for nothing but comfort, and not sexual pleasure), and is it in the Bible? Personally, restrictions on kissing sound about as logical as restrictions on where you're allowed to hang a poster on your wall.
If God didn't want us to have sexual thoughts about the one you are currently in relationship with, he wouldn't have made us part of Nature, which thrives on reproduction. Having said that, people may say that it's a test of temptation, but honestly, thoughts are thoughts. If God were to control our minds to get rid of these thoughts, free will would be void. So, if you have these thoughts, you aren't tarnishing God's name. You're being human. Just don't act on them, 'kay?