I would say that it would be Neptune-Mercury square or opposition that would cause many misunderstandings and confusion that could be perceived as lies. It has to do with communication.Neptune square or opposing personal planets really can damage relationships. I know a couple with Neptune opposition Moon and their relationship suffers because of it..this describes it perfectly..
Neptune opposition Moon:
What does it mean to your relationship when your Neptune is in opposition to your partner's Moon? You want to fit him/her into your romantic ideal which makes it difficult for your partner to express his/her true feelings. If your partner's Neptune is in opposition to your Moon, he/she doesn't fit your idealization of your romantic expectations. Idealism, fantasy, and imagination permeate the atmosphere between you and your desire leads you to believe what you want to believe. Your souls are spiritually linked, but you have two different approaches to romance and relationship and these are reasons you are together to work it out.
Cafeastrology says it like this:
Opposition Moon - Neptune
Negative aspect: This union will be full of illusions and disappointments. They will find it difficult to understand each other. Unfaithfulness and lies are on the agenda.
Ouch.
------------------
Capricorn sun / Scorpio rising / Sagittarius moon
No man is free who is not master of himself.