Like drifter said, there is no way to just make PTSD go away, it will always be there no matter how strong or happy you want or try to be. You should always be there for him, and comfort him. Ask him what you can do to help, just stay positive because it will always be hard but it's not his fault no matter how bad it gets keep in mind he doesn't have control over it like he would like to.
PTSD never goes away my advice would be to support him on good days and deal with his bad days I suffer from nightmares and flashbacks be there to hug him ok :)