보고싶어요 by itself almost always means I miss you. When it doesn't, you can know from the context. For example, "제가 에펠탑을 보고 싶어요" must mean that "I want to see the Eiffel Tower," because "I miss the Eiffel Tower" doesn't make much sense here. 보고싶다 and 그립다 are both translated to the same thing (I miss ...), however they are used differently. When using 보고싶다, the thing/person being missed is the object of the sentence; whereas when using 그립다, the thing/person being missed is the subject. To illustrate the difference, compare 1) 내가 너를 보고싶어요. 2) 나는 네가 그리워요.

I'm not a native Korean, but I've learned it quite a while. So I'll try to answer this question. 그리워요 means "missing you" or "longing for you" while 보고싶어 usually translates as "I miss you". So you can say that 그리워요 is used in a more serious/deep-meaning sentences. While 보고싶어 is used in a lighter way/lighter expression. Ah, I hope this helpful.