Hi H....
Speaking from expierence....this situation SUCKS! The worst part being, there is nothing you an do to make the ex want to have a relationship with you. If I were you I would just stop trying, if you are anything like me it's probably just stressing you out. Just go about your life being who you are and not worrying about her. As long as you are taking good care of her kids and respecting the basic rules/guidelines your husband and her have decided about co-parenting then you are doing everything you can. I am going on 12 years with this situation and I think we finally have all come to a "safe/comfortable" agreement on what works communication wise, for us...we only communicate thru e-mail:)
BTW for us things went like this: Ex wanted him back (called repeatedly and tried to steer the conversation this way), Ex was mad he didnt want her back (anything and everything was diffiult, she really mad our lives hell), Ex now pretends he doesn't exist (sure it sounds great but in all actuality it sucks, she does not include him in anything,most of the e-mailing is between her and I).
One last note the ex was already remarried when I entered the situation and it still went this way, if your ex is still without a significant other I imagine your situation is going to be difficult for awhile longer...sorry!
K.