Sounds really tough, BP.
Look after yourself. To me, your post reads as though you feel that you alone are responsible for E's dishonesty. Your words read as if you think that if you were different, softer, better able to deal with E, he would feel more at ease and would not behave in the way that he does.
I worry that this isn't the case. You don't and can't control how he responds to stress in his life. Only he can. His choices are not caused by your behaviour - they are his choices.
I think that he does have a habitual way of dealing with problems which is hurtful to you. Unless he does a whole ton of work, his habits will remain. Habits tend to do that - even if they are destructive and even if we don't want them to.
Look after yourself and if going behind your back to talk to Sync (or anybody else) is a deal breaker for you, I think that you need E to be owning his habits and doing the work needed to change them.
Good luck - sending you a hug. xx