You're going to have to get past this hang-up. That's what therapists are there for, and they have heard it all. You can't really manage this by yourself so your only real option is to open up to a professional.
Given your trust issues, though, I am suprised you've chosen a long-distance relationship. Those inherently require an even greater level of trust since you aren't around each other as much, and yet trust is your number one difficulty.
How did you meet, and how often do you see each other in person?