Why did he do it?

So my partner was in an accident about 18 months ago where he jumped a fence and crossed a 6 lane road which resulted in him getting hit by a car. He suffered with a bleed on his brain and so he doesn't have much memory of the actual accident. He keeps sitting up late at night thinking and trying to remember what made him decide to cross the road. He's come to the point where he thinks he was trying to kill himself but I don't believe that. He's suffered with depression after the accident but was a very happy man before the accident