Russell, it is difficult to forgive someone who does not exhibit remorse, however I do believe that forgiveness is for us, not for them, so we don't harbor that bitterness in our hearts.
Trust is earned, your son has not earned your trust.
It is imperative to impose boundaries on the choices and behaviors of our adult difficult kids. While your son may not be seeking any help, it may be prudent for you to seek help. We can't change, fix, control or in any way, impact the choices of our adult kids, all we can do is learn to respond differently and take care of ourselves. It is such a different and difficult new way to parent that often we need help in figuring out how to do that. I know I did. I needed a lot of help.
Since your son is bi-polar, you may find support at NAMI, the National Alliance on Mental Illness. They can be reached online. They offer excellent courses for parents which will give you information, resources, guidance and support. They helped me so much with my daughter.
You might read the article on detachment at the bottom of my post here, it has a lot of useful information.
We never help our kids by enabling them. And, many of us are not clear about the difference between enabling and loving kindness. It takes all of us awhile to learn that difference, which is often where professional help comes in.
Our kids behaviors put us in the awful position of having to make those hard choices you are referring to, not an easy task, but almost always, a necessary one.
Hang in there, get support, keep posting, it helps. We know how you feel, we've all been in your shoes.....glad you're here....