How about....
'I'm struggling to understand boundaries. I know that you are a professional and have to maintain some sort of distance but I've come to value and respect you and want to consider you as a good friend. I don't know if that is possible given the circumstances? Sometimes you respond and willingly offer help and support and other times there is no response. I'm finding it really confusing and emotionally draining when trying to work out how to react. Because I respect you I would really like to hear your thoughts?'

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