I think there's more than to it than "TRUST". More of it is effort and sustained mutual level of interest.

In my opinion, the issue with long distance relationship is complicated. It's more than just trusting. There are things like nostaligia, lack of overt sexual expressions, physical presence and etc. that trust can not handle

things like these don't thrive on trust. they thrive on presence. and that's why long distance relationship as the write clearly stated has a unique challenge.