Honestly, if he has no legal responsibilty then she has no legal obligation to plan around when he takes their son. Honestly she should consider treating the situation as though he does not exsist plan for a sitter, or relative, etc. to watch him. If Dad happens to show up then cancel the sitter. Just let the sitter know the full situation in advance, this way there is no misunderstanding. This way if he bails at the last minute it doesn't ruin any plans, but it also removes the impact of any spitefulness that may be going on.

The downside is that there is and will probably to continue to be some serious pain and hurt for her son. In that regard, you should try to be as patient, understanding and supportive as possible for both of them.

After seven years I still have those problems with my ex. But I have learned, as I am sure she will in time, that if you want to have a normal life while divorced with kids you need to plan around your ex, not with your ex.

Single parenting can be challenging enough without adding dating into the mix. I suppose the issues you're experiencing is part of the reason a lot of men won't date single mom's. My suggestion would be to be as flexible as possible. One thing about being a single parent is that you can be stressed out from doing everything yourself. Offer to pamper her. Tell her you'll pay for the sitter and then whisk her off for a romantic night out. Casually ask if she has any relatives who can watch her son when dad lets her down or if he could have a sleep over with a friend.
Try to stay clear of the issues between the ex and your lady. Let her take care of those issues. Just continue to be a bright spot in her day!

Well, the thing is when you are dating someone with children, you have to have patience. A spark is hard to find these days, so I say its worth it! Can you imagine how stressed she must be, but its one child and thats not much to deal with. You can continue to see her, just take your time and try not to rush things and you will soon find out what to do.

Therein lines the problem. She does have full legal custody, hence full-time responsibility. She also doesn't fully trust the ex-husband, but what mother would deny her own child time with his biological father? That 100% custody is a loophole for the ex to not have to accept responsibility for his son.

So the question remains... How to keep the ex "on task," so to speak, even though he is under no legal obligation to do so?

I have partial custody of my daughter, and her father has continued to make it increasingly difficult to schedule times to see her, and when to drop her off, etc. But, if she has full custody, legally, she can deny him parenting time if he can't commit to a set schedule, or even, leave her son there as long as she needs. My best advice is to do what is best for her son. I wouldn't know what that is, i'm not her. If she has sole physical custody and he has partial legal custody, then there should be a contract of parenting time done. If he doesn't exercise his parenting time within the limits allowed, then he does not get to exercise them.
He's probably just being petty, because there's a new man around. Give him time to get over it, and if you really like her, try to be patient.
I hope this helps.
-Mikaela