I'll start off by saying DH works every Saturday 4am-2pm. I watch the skids while he's at work. I volunteered to do it, and I *generally* don't mind doing it. HOWEVER.
I have friends in a band. They're playing Friday night. 2 weeks ago BM said she was taking the skids Saturday. I had DH ask if she'd take them Friday night so he and I could go see our friends play.
She replies with she'd *maybe* take the kids Saturday. She has PLANS for the weekend.
FUCK YOU BM. DH AND I HAVE HAD YOUR CHILDREN EVERY SINGLE FUCKING WEEKEND FOR THE PAST FIVE MONTHS. While she's out partying. She'll even go out after work, while her boyfriend of TWO MONTHS watches the kids on the weekdays she "has" them.
This weekend DH is working 10 hour days BOTH SATURDAY AND SUNDAY. Which means I HAVE THE KIDS ALL FUCKING WEEKEND ALONE. She replies to DH, "It's not my problem on the weekend." EXCUSE ME? They are also YOUR children, which means they are ALWAYS YOUR problem. "It's not my job to give funmommy a break, it's yours."
YOU CAN KISS MY ASS BM.
So, BM, what I would like to say to you
From now on, I will pick the kids up from school. You don't do it anyway, you have your boyfriend or sister do it for you.
I will keep them every night. Maybe if they stay with me they'll actually have some fucking stability in their lives.
IF you ever feel like you want to STEP UP AND BE AN ACTUAL FUCKING PARENT you can take them on A FUCKING WEEKEND.
So I guess you'll never see your kids, because your PLANS are more important than actually spending time with them.
Oh, and since we'll have them so much, we'll slam your ass with child support. You don't buy shit for them anyway.
I would so LOVE to tell your kids where your priorities are. Sadly for me, I'm not a bitch like you, so I won't do that. I'll wait until they're old enough to see it with their own eyes. And they will. All of their FUN memories of doing things, seeing things, will be with me and DH. They already are.
You can GROW THE FUCK UP and take YOUR kids for a weekend. It won't kill you. I have half a mind to drop them off on your doorstep and tell you, "It's not my problem EVER."

And DH, I get that you get sick of dealing with her shit. HOWEVER. This doesn't affect you NEARLY as much as it affects me this weekend. Telling her you're sick of her shit and done dealing with her, DOESN'T FIX THIS SITUATION. And you are LETTING HER DO THIS by giving up.