Banned from stepsons grad party?

My husband just got an from his ex wife. She has banned me from my stepsons grad party. She said I would cause problems and maybe make things explosive. This all started from a comment I made on my stepdaughters facebook status. She is 22 and an adult as is my stepson. The comment I made was not mean in anyway. She called her Mother saying I had attacked her and the family in turn the Mother started posting things on facebook that I had attacked the family She also sent my husband an email that said he was a bad father for not having his daughters back. I have seen her at a few gatherings since and we just ignore each other. So for her Mom not wanting me at the party seems strange. I get along great with my stepson and my husbands half of the family are all going. My husband plans to still go and wanted to take our 2 small children with him. I don't want my kids around this person who seems to really dislike me. Also my husband said he won't do anything about it since he does not want to be in the middle of it. I am very upset that my husband did not stand up for me in any way and still is going. I said we could have a party of our own for him but my husband said no and it really bothers me that he seems to think it's my own fault. The Ex wife also told my husband not to discuss this with their "children" who are both adults. I feel angry at my husband almost like he won't even try to stand up for me. Has anyone any advice?