Look, I might sound a bit black and white but I really believe that his ex can only be a pain if you and your beau allow her to be one. Why not discuss your family changes with her and then see what kind of reaction u get. Maybe she will be fine about it when she realises that she has no say in it all. If she isn't ok with it then I think u then need to reinforce to her that u r not asking for her aproval or blessing merely being considerate of her feelings and that if she doesn't want to come to the party, then basically bad luck! This is your life with your partner, she had her chance and he has moved on. Wether or not she is a willing player is neither here nor there. You go ahead and have the life you deserve, u only get one shot, stop worrying about her feelings so much and start worrying about yours and your partners. Be happy!

Best of luck, Jo xx

         Sounds like a tough situation that your in, but you know it really doesnt have to be all that hard.  If you and your partner are serious about each other then you will make it work. I Don't mean to sound cold hearted but this is my story in brief........When my partner and i first met, he had two children to a previous relationship and i had my two to my previous partner.  Yeah sure at the start it was really tough because his ex never wanted anything to do with him until she knew that we were serious about each other, then it all started  the phone calls, the tears, the kids need this, need that etc etc etc, it went on for about 18mths, we went through some good times and some really tough times trying to find our grounds with each other, on the other hand my two children and him were bonding beautifully, I bit my tounge and encouraged him to see his children, so we did and from that day on the kids mother has moved on and moved away, my partner can see his children whenever he wants to.  After two years into the relationship my kids father decided he no longer was needed in their lives and decided to have no contact with them, which really upset my kids for a little while.  Over time my kids havnt seen their father for 4 years (his choice only) , my partner and i have been engaged for the past 4yrs and will be getting married in October this year.  We also have our own two children together  now

,  who are 20mths and 5mths old, so bottom line is ....... you can have a sucessful relationship with blended families if you are both prepared to take the good with the bad and stick by each other ......you can go far.......Phew i can now take a breath, sorry theres no punctuation in this article as i have typed it in between feeding etc, etc. 

                                                         Cheers