This is a tough lesson to learn (I know -- I was (and still am) a lot like you), but you cannot "make" ANYONE happy. They have to make themselves happy.
One thing I have learned is that while I could not have MADE her happy, I could have done so many things to let my W know I loved her. I dropped the ball on that. I think you can at least HELP someone be happy and you have a responsibility to do so for those you love.
~Mark
Me: 38 W: 34 Together: 9yrs 1st M: may '03 1st D: april '08 1st bomb: june '08 remarried: oct '08 2nd bomb: aug '09 --(W asked for D one week into 3 mo. trial separation which was meant to save our M)