Divorced w/kids.... and new relationships

Hey - i’m looking for some honest feedback related to my current relationship. I have been dating a divorced man whom has 2 kids, ages 4 & 6. He has been separated from his ex wife for almost 3 years. The custody arrangement is nearly 50/50... with her having them a few extra days out of the year.

I have been dating him for nearly 5 months... and in terms of kid interactions, we took it very slow in the beginning. I met the kids at a kids birthday party after 2 months... then waited 2 more weeks before meeting them again (this time he and I took them to a Kids fun house)... then after that a few more weeks... etc etc. His kids seem to really like me - when he Skyped them the other day - they wanted to talk to me... and whenever I am over at his house - we play games...

So now... this is where the drama comes in... My BFs ex found out about me and she wants to put an order in the courts that the kids are not allowed to see me or hangout with me if my BF is not around. She also wants to prevent him from ever having me spend the night when they are at his house.... yes, there is more to the story then this...

No, I have not done anything nor does she no me personally. I have a good job... am well educated... and am kind natured...

What happened was - though I rarely spend the night when his kids are over... a few weeks back, I did because it was late. In the middle of the night, his youngest came down and jumped in the bed next to me. The youngest is very comfortable with me... and I would say we have a friendly relationship...

And no... my BF and I do not have sexual contact when his kids are in the house (as I know this is going to come up)....

I guess what I want FB in... is I could understand and mom being concerned about a new dating partner.. but is she overreacting OR am I underreacting?

I think part of her issue with me is that her kids like me.. but I do understand the concern... but not her reaction to threaten my BF with new court orders and a threat to try and renegotiate custody? I just don’t want to cause him or the kids and harm... hence why we have been slow/careful... but I also do t know what I could’ve done in that situation asides from kick his kid out of the bed (which would have been worse)...

Thought? Am I missing something?