https://us.forums.blizzard.com/en/wow/u/name-realm/summary (replace name-realm with your character name and realm respectively), also can be seen by clicking the little char icon in the top right of the forums, clicking your character name, then summary.
Shows counts towards the trust level as far as days visited, read posts/time, likes, and your current trust level (member is trust level 2, regular is trust level 3, don’t remember what trust level 1 is)
Also there is a stickied thread on the forum that outlines the exact things needed to get TL3 (though not to ‘maintain’ it) at New Forum Guide - Syntax and Features
That said, I personally agree with the trust decaying just from being inactive being a bit sad