Sure, 'I Love You' is just a three-word phrase that we tell at our friends or yell to our dog every morning before we leave the house, but it is actually a really heavy subject.
Honesty is the best policy.
You could say something like 'I care about you too' but people can be hurt when you respond to their confession with a less powerful word like 'like, care, etc.' Tell them straight up that you just aren't ready to say that yet - but that you feel like you are getting there.
And if you aren't feeling like your affection is growing at all, why are you in the relationship to begin with?
If your partner really does love you, they will wait for you to be ready. Sure, they might have hurt feelings but they should respect and understand where you're coming from. They should honestly and completely love you too.
This was my favorite response that I've heard so far:
"I think I'm falling for you too. It's too soon for me to say if I love you but I'm falling."
And if you need a Norwegian pop duo to explain your feels, here you go.