Maybe next time you could explain why it is not possible to pick up your child, i.e
'I'm sorry W but I can't because I will be late for work, however on such and such a time, I can help you out.'
Meet her half-way. This is your child too and it's not fair for either of you to involve that child in your M problem. It isn't his fault. However, I agree that you shouldn't be at her beck and call every time, just there for your child as is reasonable.
She has to learn to act like a single mother to a degree, with all the responsibilities that come with that. It's striking the balance, though.
I totally understand why you feel used/hurt etc. I have felt like that too.
