Of course you can't be open and honest with everyone. That would be childish and immature. Everyone in your life is on a need-to-know basis. Everyone! That includes family members and friends. And, you definitely don't want to give intimate information to gossipers and strangers. That said, someone you intend to marry needs to know your relationship history. If they are not worthy of that information, then, neither are you worthy of marriage where two people become one. People who hide usually have very smelly and nasty rooms that they are afraid to open. Thus, they can never heal and they make relationships with others impossible. Without confession there can never be healing. Furthermore, they will repeat the performance shackled by their past. Open and honest i.e. being transparent, is not optional, it is an absolute necessity to having a growing and successful relationship.
"For every one that doeth evil hateth the light, neither cometh to the light, lest his deeds should be reproved. But he that doeth truth cometh to the light, that his deeds may be made manifest, that they are wrought in God." (John 3:20-21)
"Confess your faults one to another, and pray one for another, that ye may be healed. The effectual fervent prayer of a righteous man availeth much." (James 5:16)
"The wicked flee when no man pursueth: but the righteous are bold as a lion." (Proverbs 28:1)