As a mono new to all this, and having been cheated on several times, sexually and emotionally, I am just sorting out all my fears and jealousy...
Because of the cheating, and its obvious sexual nature, I *thought* that sex was the bigger trigger/perceived threat...it certainly brings up issues of inadequacy, and of being abandoned. But as I start to dig deeper, and as I realized the depth of the emotional connection underlying the sexual realtionship, I am finding that it is the emotional connection that I struggle with a lot more - it just gets magnified a lot more when sex is also involved.
I find the emotional connections bring up more fears of being abandoned, and of not measuring up (more inadequacy), but in different ways. And everything is heighted because that emotional connection is pretty much constant, in this time of texts, IM's, emails, video chat, etc. Sex, while fabulous, cannot be constant, it seems to ebb and flow, while the ever present emotional connection seems to flow into every corner of one's life and grows and grows. Though, as I said, when the 2 become one...that is hardest for me.