Single parenting is difficult even under the best of circumstances, and my heart goes out to anyone who must bear the burden of parenthood alone, regardless of the reasons. I want to assure every single parent who is reading this that God knows what you're going through, and He cares and wants to encourage and help you.
Thankfully, those days are now over for you and I suspect you did a far better job as a single parent than you think you did. Elsewhere in your letter, you mention that your other children are now grown and doing well with their own young families. You must have done something right!
In other words, your example of perseverance and hard work has influenced them, and you should be encouraged by this. The Bible's advice to pastors could apply to parents also: "In everything set them an example by doing what is good" (Titus 2:7). Your son alone is responsible for what he did, and you should not bear a burden of guilt you don't deserve.
At the same time, I urge you to turn to Christ and build your future and your family's future on Him. Confess your sins and failures to God, and from now on make Christ the center of your life. Then let your son know you still love him, and you pray that he too will find Christ's forgiveness and peace.