Your situation is very common. Their emotions fluctuate. When he is decent, notice it, relish it and compliment his choice to be this way. You are worried about not trusting him, well why should you? Trust is earned and it takes lots of time. Just when we think their behavior will be consistent, they turn again.
Me: 46 H:44 Together: 25 years Married: 20 years Separated: 11-30-06 Divorced 12-21-07 OW: EA began 2005 PA began end of 2006 3 children,20, 16, 6 ex asked for forgiveness 01/16/11