If you do not want to be in a relationship either just don't agree to be in one, or overcome your fears by taking it slow with an intent to mature. I used to have some of the feelings you described (like- how can you feel like a good person afterwards etc.) and the reason behind that for myself was fear and guilt related to abuse in childhood and the belief system that I was born into. As time goes on though, you will grow past this if you work on it. Perhaps you SHOULD actually be friends beforehand lol, you would at least know the person well enough to make a sound decision and be able to gauge their personality and character enough to know they would not mock or condemn you for being with them.