Should I tell about my past sins to the person i will marry?
We are serious with the person I love, but I am not the kind of person who would suit her/him with honor, s/he is a much more pious person. Should I tell her/him I committed adultery? S/he may not want me when I say it, and I am ready for it, but I do not want to do something that Allah does not want. Should I be honest?
First, are you a repentant person? If you are not repentant or do not protect your repentance, your priority should be repentance. If you repent and keep your repentance, you are worthy of all purity, because after repentance you are also clean. As for the matter of telling him, don't just say you committed adultery. Tell him that your past was full of dark days, but you took refuge in Allah with repentance. However, if s/he accepts you, there is no problem.