Complex sentence: It is quite reasonable to take an interest in an article on a topic you care about--perhaps you are an expert, or perhaps it's just your hobby however if this watchfulness starts to become possessiveness, then you are overdoing it.
Split into simpler sentences: It is quite reasonable to take an interest in an article on a topic you care about--perhaps you are an expert, or perhaps it's just your hobby. But if this watchfulness starts to become possessiveness, then you are overdoing it.