Do not ever hide anything from him/her. Especially your health, feelings about him/her and your relationship - whether good or bad! This way you will be able to overcome all the difficulties and challenges together. If something bad happened in your past that still affects you in the present, he/she needs to know about it. Note: you should be able to discuss your sexual history. It is an obligation before you decide to be sexually involved with your partner. But you should make them feel safe and not judgmental and you should expect the same from your partner.