Disrespectful behavior will repeat itself as long as you allow it. As nice as you are, you must have boundaries for your life set in place as to what is acceptable from others and what’s not. People sometimes tend to confuse ‘niceness’ for weakness and for mere stupidity. It is always best to be nice and polite as a good attitude would open amazing doors for you, but absolutely, positively, without a shadow of a doubt — Have A Backbone. Stand up for yourself when necessary. You are worth it: You are worthy of respect.
You cannot be everything to everyone. The sooner you figure that out, the more at peace and better off you’d be.