Formal:
* Я дуже сильно люблю тебе. (Ya duzhe syl'no lyublyu tebe.) - This is the most direct translation and is appropriate for formal situations.
* Я щиро люблю тебе. (Ya shchyro lyublyu tebe.) - This translates to "I love you sincerely" and is also appropriate for formal settings.
Informal:
* Я тебе дуже люблю. (Ya tebe duzhe lyublyu.) - This is the most common way to say "I love you very much" in informal settings.
* Я тебе обожнюю. (Ya tebe obozhnyuyu.) - This translates to "I adore you" and is more passionate and intense than "I love you."
* Я без тебе не можу. (Ya bez tebe ne mozhu.) - This literally translates to "I can't without you" and is a very strong expression of love.
The best way to choose the right phrase depends on the context and your relationship with the person you're talking to.