I have a teen son, but my BPD ex is not his biological father. That's another story for another time

Mine is an ongoing thing. I got into a verbally abusive relationship at age 20. Lasted for 13 years, it was hell. I managed to get out by moving 1500 miles away from the guy. To ad insult to injury, I got involved with a narcissist, the biological father of my son. That lasted for 9 years.
He was not as bad as number one, but bad enough. As I was getting out of that mess, I got to know my ex BPD. He was everything a girl could dream of and everything I needed for my bruised ego.
Long story short, we got married. He was everything I needed at first, then the whole BPD process started and a dream turned into a nightmare. I am ashamed to say that, in the end, the only reason I stayed with him was that I was afraid I could not make it on my own, financially. I have a teen son and am in my fifties and I thought we would go down financially, without my ex.
In the end, it got so bad, I did not care about the financial consequences anymore and I asked my ex to leave, moved all his stuff to the garage and some time after that, he started divorce procedures. We sort of mellowed out and tried the friends with benefits thing. I felt horrible, like I was seeing a married man. And I still had to deal with his BPD issues.
I told him I could not do this any longer and we had one last conversation, where he went into the biggest, most awful rage I had ever seen. Since that night, I have done the NC thing and it works for me.
I went into counseling and it was an eye opener. My counselor had started his career at a penitentiary and a large percentage of the inmates were either BPD or narcissistic. It helped into seeing that it wasn't me, at least the largest part of it was not me. But I still have my moments of doubt about that. My ex BPD did a lot of damage, gradually, year after year, and you don't just undo that in months.
Ex shows interest in my son when it suits him and when he feels the need. He can go months without contacting him. I discussed this with my counselor and we agreed that my son would be okay to spend time with him, as long as it did not hurt my son. Quite frankly, I think my son is better at taking my ex BPD at face value and enjoy the fun he can have going camping and hiking, but not having any high expectations when it comes to consistency. My son knows that my ex has never been and never will be a constant in his life, but sees my ex as this fun, crazy uncle that shown up every couple of months with totally inappropriate gifts, telling totally inappropriate jokes.
As for me, I am adamant in the NC routine. I will monitor any contact between my son and my ex BPD, but I do not communicate directly with my ex BPD. He will send me emails about how he tried to call my son, I will tell my son, but not reply to my ex BPD.
I believe he has a GF right now. My worst fear is that my ex BPD will try to get back into our lives when she dumps him (notice I said when and not if, because she will). It is a pattern that he will follow. I left him a couple of times, he would try to get back into his first two ex wives lives. My counselor told me to call him if and when he tried to get back into my life. That, and if and when I met somebody with whom I thought I might be starting something serious in the romantic field. Guess after three bloopers in a row, he thinks I need a bit of help in telling the good guys from the bad guys, huh?
My son, at age 10, told me, "Mom, do you know that you have a tendency of picking very immature guys? Maybe next time you get to know somebody, send them by me first, so I can check them out". I think I will do just that... .
