How do you write you love Lynn in Japanese?

In Japanese, this would be: "totemo ai shiteiru" (とても愛している) or possibly "hontou ni ai shiteiru" (本当に愛している). The first is "I love you a lot", the second would be "I really/truly love you".

Note, some people might tell you to use "watashi wa anata wo" before those, and while they're technically correct, don't listen to them unless you want to sound like you're reading aloud from a textbook. Real people don't talk that way.