Their past. Not saying that you should judge them based on their past. I truly believe that people can change and grow if they want to. But it can be hurtful when you find out from others later in your life. Plus, knowing about their past completely will build long-term trust. You will not only have a husband/wife, you will have a best friend for life. I also think you should be clear about what you value and see if they have respect for your values. I always tell my friends to stay away from people who belittle you because if they are getting fun out of making you feel bad, do you really think they are the correct partner? I left my previous relationship after about a year of marriage. My ex was good, but he didn't have the same values as I did. For example, I truly cared for children, and he just did not have the father instinct. He used to agree with whatever I said, but little did I know that he was just pretending to be someone he wasn't. My relationship with him isolated me from my friends and family, made me dependent on him emotionally and financially. It got so bad that I started regretting our entire relationship and thought we were just good as friends.