If only you knew how much I want to be part of your community. Or If only you knew how deeply I want to be a member of your community. These sound natural and sincere. Saying it like this supports the heartfelt tone you are going for, as suggested by the emoji put at the end of the sentence.

It sounds natural, but it a dependent clause, not a sentence. You can say it, but if you write it, you need to add an exclamation mark: "If you knew!" "If you only knew!" "If only!" "If!" No special structure is required for an exclamation - only enthusiasm.

If you knew how much I wanted to become a part of your community, you would....