I found the following in A Dictionary of Latin Phrases, by William Robertson:
Haeres mihi in animo
You are dear to my heart
A more literal translation would be "You adhere to my heart," or "You are impressed on my heart."
To address your concerns about whether this might be used in a non-romantic context, I found a very similar expression used in such a context. In fact, the only diference is that this second expression has in medullis instead of in animo, but they essentially mean the same thing. The phrase in medullis literally means "in [my] inner parts", but it can be equally (and more naturally) be translated as "in [my] heart", or in this context, "to my heart."
Anyway, what I found is from the play Orestes, by Wolfgang Waldung. Here we have Iphigenia speaking to to her brother, Orestes:
Oresti, fratri meo longe dilectissimo, […] haeres mihi tu in medullis.
Orestes, my most beloved brother, […] you are dear to my heart
So, as you can see, the expression Haeres mihi in animo, or alternatively Haeres mihi in medullis may be used to express the love between family or friends.