It came from a thread of someone asking for his picture to be edited to have flames in the background. People started messing with him, and then someone made it into a macro. It happened only yesterday and it's already been shared on multiple websites and people have been making others.

Due to its significant similarity to Good Guy Greg, multiple contributors brought up the idea of changing the format of the meme to instead open with some form of a promise, followed by "TRUST ME".

Origin: http://chanarchive.org/4chan/b/40826/

More Trustworthy Trevor: http://www.quickmeme.com/Trustworthy-Trevor/popular/1/?upcoming

Also, I found a post on some Maplestory forum. The OP seems to be the guy in the picture.
http://www.demethos.eu/forum/showthread.php?3022-Look-what-Liam-(DevilRain)-gone-done-did.