There will be something mysterious, even confusing between you. It might be that you just can't see your friend for the person they truly are. The problem could be as difficult to pinpoint as it is to understand, but you'll both feel the effects.
Your pal may insist everything is fine, even though both of you know that's not true. Or they might make a judgment of you -- not a positive one -- and then deny it or change the subject when you try to get it out in the open. In some way, hidden emotional influences will affect your relationship and you'll have a hard time talking them out. The best way to deal with this might be just to make sure that each of you asserts your individuality. Neither of you should submerge parts of your personality just because you think your friend might like you better if you do.