"I trusted Gurlak but then he betrayed me."
Translation:ghurlaq vIvoq 'ach ghIq mumagh ghaH.
It's a problem that they both often get translated as "then". vaj has an implication of one thing resulting from the other and is better translated as "thus". ghIq has an implication of a change happening at some point in time and may be better translated as "subsequently". This sentence is definitely talking more about a change that happened at some point in time and not one part being the consequence of the other.