Mmmm I think very much depends on the relationship and communication. In my marriage to my husband clear boundaries were very much needed and respected but with my wife it's not needed as we know one another dislikes and triggers so 'no' is very rarely used normally in jest than anything else . X
For me being too nice has previously lead to being taken advantage of, walked all over and then abused - mentally/emotionally/financially & then physically. In the relationship there was no saying no because he was the priority- not our babies, not keeping a roof over our head or holding a job. And when I did try to establish healthy boundaries (even early on)I was the problem, I needed to change, or whatever was going on was my own fault/doing. So yes I know there is such thing as being too nice.
I believe so. I don’t remember exactly how it went down.. My husband as always put me first and did everything I wanted. Then one day, he told me otherwise. I did get upset but our relationship actually got better after having that discussion/conversation.