Where is the Rule Book?

Something that has crossed my mind lately is that there are no rules in relationships.  Sure, there are dating rules, such as guys feeling pressured to pay for dinner, or when you propose, you are supposed to bend down on one knee.
But I am really focusing on the ways that we talk and communicate with each other.  There really are no rules; no set guidelines telling you, don't say that or yes that is a great thought to express.  Where is the red line drawn that states that if you say this, you will be throwing too hard of a punch or pressing on a vulnerable button?
There is no referee whistling for a time out or handing out penalties.  There is heart break and comfort zones crossed to the point of no return.

Therein lies the fear.  What if you overstep an invisible boundary line?  What do you do with the damage that you cause?  I have no clue.

But then there is the virtue of crossing boundaries in a loving way that reveals raw communication.
The raw communication being two humans, stripping down to the doubt and emotion that we hide from the everyday world.  Romantic love, friendships, family, or mentors; I don't care what relationship it is; the root of the point of these relationships is to see that we are all together burdened by our fear, shame, insecurity.  When we share these vulnerable thoughts and look at each other with clear eyes, we love.