1)
What was consolation in his affliction?
1.
Radak: When I was exiled, this hope 1 was my consolation.
2.
Malbim: Even though I am afflicted (he said so when fleeing Avshalom), Your promise consoled me.
1
I.e. the promise via Nasan ha'Navi, like Rashi said in verse 49. (PF)
2)
Why does it say "Chiyasni"?
1.
Radak: I would have died of sadness, if not that Your words and promise sustained me.
2.
Malbim: I remained alive and did not fall in Avshalom's hands, due to Your words and promise.