I think lying and willful omission are painful because they imply that the person you are keeping something from is unable to handle you or the situation.
If you don't allow the truth about yourself to be known, you can't hope for another person to understand or support you.
When you make a habit of lying or willful omission, you communicate that:
1. You don't feel that you and your life are acceptable and
2. You don't trust or respect your partner to handle things.
So your partner comes to have that imbedded in their perspective of your relationship and will probably:
1. Not fully accept you for who you are and
2. Not trust you, or maybe themselves, and not be able to handle things.
"Rocks will open and make a way for the lover."
~Hazrat Inayat Khan
I love Catfish and Charlie.