Even if you used a past tense, that doesn't mean that you don't love her now. Falling in love with someone can have a short duration so as an action happened in the past you can use the simple past tense without problems. (I think you wondered whether you should use "I fell in love" or "I have fallen in love". "I fell in love" is fine). The sentence doesn't give info about the current status. It may be that you fell in love with her and you still love her or you fell in love with her but now you don't love her anymore. It isn't specified in the sentence so it could mean both. If you want to make sure the other person that you still love her you could specify it clearly by adding a few other words.