If you can not have a civil debate with someone who is supposed to be your friend (romantic or otherwise) then you are better off without that person in your life. I would never hold back my thoughts or opinions out of fear of upsetting someone. Any relationship needs honesty and openness in all aspects. If expressing yourself is going to cause you to lose a relationship then so be it. It's better than living a lie or keeping your feelings in check for someone else's sake.