I read your post several times over before I decided what I was going to say.
Joanna, I truly feel for you.......we mothers worry the whole time we're raising our children, and just about the moment we think we can stop, they become adults with their own lives and then the REAL worrying begins! We no longer have a say-so in what they do, and having to give up control is a killer---especially when they conduct their lives in such a manner that causes us concern.
I think you did the right thing by refusing to allow yourself to be used. You've done your time as a fulltime mom, and you've earned the right to decide how YOUR time will be spent. But I don't think your daughter is really 'playing' you.........she is literally torn between you and her loser husband, and even though this position is somewhat her doing, I feel she needs some moral support from you, because she certainly isn't going to get it from HIM. That doesn't mean you have to get sucked into the vortex, or play into his games.........in fact, if I were in your shoes I would simply ignore his existence entirely, at least as much as it's possible to do so. He is a worm who deserves neither your attention nor concern.
Your daughter (and your grandson!) do deserve those things, however, and here's where you've got to be careful because you don't want to alienate her, or push her further towards the husband. She's at a cross-roads right now; in her heart of hearts, she KNOWS the marriage won't work, but she's frightened and she's hurt and she must try to save face at all costs. This isn't about you at all---it's about her fear of failure, of being alone, of having to start all over again.
She's what, 25? That's not a vast age.........she hasn't even begun the process of becoming self-aware yet, let alone learned how her actions affect other people. She is probably easily manipulated; when she 'turned' on you the way she did, it was more than likely because HE got to her and talked her out of her plans, not because she wanted to hurt you. She sounds to me like a very mixed-up and confused young woman, and she's in a tug-of-war. Your job, right now, is to let go of your end of the rope---be there for her, be supportive and as non-judgmental as you can possibly be, and DON'T attempt to talk some sense into her. She's not ready to hear it. Someday he will make one mistake too many and alienate her for good, but that time, obviously, has not arrived yet...........and there's nothing a mom can do to make it come any faster.
I am so sorry this is happening to your family. I know you love your dd and grandson just as I do mine, and my heart hurts for all of you.
Of course, if you feel your SIL may be a danger to your grandson because of drugs, none of this applies.........that's when you call Childrens' Services and report him! No one, not even a natural parent, has the right to bring cocaine or other illegal and/or harmful substances into a home where small children live.
Wishing for a good outcome for all concerned.:icon_hug: