Blending Families: why can't we all just get along? Jealous ex and slightly insecure gf.. what to do?

Let me begin by saying I am very blessed and I love my man and his six year old son very much. I know we have what it takes to be a great family. The "problem" is the boy's mother. She is filling the shoes of "crazy ex". She began haring me when I became the girlfriend... beginning with death threats, then to kidnapping her son for 3 months until a mediation was forced... During this time she said his father was neglectful(he is with us every other week... same amt of time and support from each parent) and is having child support taken from his paychecks.... A yr and a half later no more threats to me just a sheer understanding she will do everything to torment my man because of me in their lives. The thing is she lost control when I came in the area. My man just tries to keep everyone happy for the kids sake(which I see how hard this is for him and I want to just be there for him). I am now feeling resentment that he just lets this all happen... is it really in his control?