Originally Posted by AutumnalTone
It has nothing to do with having anything to hide. It has everything to do with violation of others and respect for individual choice.
I totally agree with this.
I think some people are simply pathological in their need to share in every aspect of their partner's relationship and activities. They can't handle anyone having something they are not a part of. It's indicative of envy as defined by "painful or resentful awareness of an advantage enjoyed by another joined with a desire to possess the same advantage". http://www.merriam-webster.com/dictionary/envy