I hope you know how much I really care for you.这里how much引导宾语从句 并在从句中作状语
原来的陈述句 是 I really care for you very much .
it's time to talk about how we feel about each other.这句从句中how引导名词性从句 作介词的宾语 是宾语从句 how在从句中作方式状语
原来的陈述句 也许是 we feel about each other in this way （或by doing sth)
Seven letters...two words...that express the feelings that I feel for you in my heart.第二个that是关系代词 代替先行词 the feelings引导定语从句,并且在定从中 作feel的宾语
in my heart是定从中的状语修饰的是 feel