as long as the words could touch your heart....I think that is enough,some time some of my friends sent me a short message and asked are you okay,I think the word could warm my heart.
Yes,but this is very common,not the most sweet and 肉麻。 I miss you is very current.And I will say "I miss you "to you if I have a long time haven't talk with you too.
I am sure that your boyfriend must have said something that touched your heart,even a simple sentence like I miss you sometime could drive you into tears,right?