Hi Gertrude Douglas
You're question no doubt comes from a place of love and concern. Like
bluek9, I would be interested to know what you're dealing with and what led you to the bpdfamily.
I hope that you have been able to avail yourself to information on the board to the right

Hopefully you this will assist you in reconciling the issues you're being faced with and some strategies for dealing with supporting your son.
While you may have view about what to say to your son, I encourage you to explore what is driving you to that conclusion and the consequences of saying that to your son. You know him better than anyone else... .he may take it well or he may feel that you are trying to drive a wedge.
For me, the best support to your son, is to be as supportive as you can when and if he talks to you about her, helping him to explore his own feelings about any relationship issues he may be experiencing. We cannot chose our children's partners but we can always be there for them, lending and ear and gently guiding.
Please keep sharing, there is so much wealth of experience and support for you.
Merlot