Dear White Dove,
That was a nasty episode and I know your heart is permanently scarred. I have a lot of scars, physically and emotionally but while they don't disappear with time, they are kind of a strong point where the raw edges joined and healed. If that makes sense. I have a manipulative son who has some of the qualities(?) that yours does, but fortunately not to that degree and he is 23 now and moving forward and making his quirks and personality traits work for him (Ok, if you think Special Forces is an improvement over slacking, anyway).
With time he will grow up and that forced regret that you sense now will be real. The only thing that may prevent that is that it sounds as if he has some personality quirks that are a little beyond manipulative. I would perhaps be concerned about serious mental health issues. Once they get older, if they start drinking heavily, (seen this in my family) it can trigger bigger problems. One of my cousin's doctors said that Schizophrenia is often seen after a person begins drinking alcohol and his thought was that it triggered it(this could be a gross simplification of what was said as it was told to me 3rd or 4th hand-so take that for what it is worth).
Let yourself forgive and heal-this is part of our job as parents. Doesn't mean you have to forget that he is capable of this kind of betrayal. You still have to fortify your heart against this kind of thing. Just love him because obviously he needs it. Don't let him manipulate and hold him accountable for things he does and says.
My best to you!