I often start out as friends with my beloveds. I try not to leave that friendship behind.
One of the reasons is that friendship can serve as a touch stone when I am trying to decide if I am being reasonable.
In general I have found that if something is not something I would be comfortable asking of a good friend, it is not a good idea to ask that of someone who is more.
And if I am trying to look at how I am treating people, if it isn’t something I would do to a friend, eg using strong language, it probably isn’t something that is ok in a more inmate relationship.
I know some people think increasing intimacy is a reason to lower standards of civility and “relax”. I have never understood why you would be less careful with the feelings of those you love than you are of the feelings of relative strangers.