It can take some time for Matt to trust someone, and he doesn't trust easily. But once you have his trust, it's hard to shake it. That's one of the reasons Matt was the last one standing (with Damon, albeit for reasons Matt viewed as far more selfish than his own) when it came to saving Elena from herself and having faith that she was still in there, somewhere.

"In the gym," he answers. "We were both there when your brother killed Tyler and made him turn."