Когда признаются в любви говорят: Я люблю тебя. When we admit in love we say: I love you. Когда хотят секса говорят: Я хочу тебя. When we want the sex we say: I want you. А вообще русский язык богат различными словами для выражения чувств. In general Russian is rich any different words for terms our feels.

Without attention to sex you can use the same Я люблю тебя. When you love someone very much, you can use - Я с ума по тебе схожу. Я тебя обожаю - I adore you.

In general Russian is rich any different words for terms our feels. - incorrect translation. Right: Russian, in general, is rich with different words for explaining feelings. ( for explanation of feelings )

"I love you" means "I love you". You can say it to a child, your mother, close friedns, your husband or wife or lover. Everything depends on the context.