Well my DF and I have been together for a year now we are engaged and expecting our first (his fourth), we are completely and utterly in love, we have both been through some terrible relationships with the same type of people (emotionally abusive and very controlling).

DF ex-wife is the BM of his oldest two children as I have said before she is usually fairly reasonable and I think tensions aren't so high as she lives 12 hours away and has a fiancé now so she has quite clearly moved on with her life, she admits that her marriage was a mistake (except the kids obviously) and my DF says that even tho the marriage was bad he wouldnt change anything as its given him two wonderful children (who he wishes he could see more) and made him part of the person he is today.

The BM of his youngest (ATM) is a whole different story... When he met her she was on her best behavior he had a well paying job and a respectable social standing in the community due to his family. It soon changed after the got together she started to try and control his money telling him 'you aren't responsible enough to handle your own money I will do it' (he is in charge of finances in our house as I'm hopeless with a budget), she wasn't happy with how he dressed so spent his money to buy him clothes she could be seen in public with him (her words), he had to keep his hair at a certain length and have no beard at all ( he is the type of guy who grows a full beard in a day!), smoking was strictly not allowed (I know it's not a good habit but I don't believe in forcing people to change who they are I would rather encourage them if they want to change).
So the point came when my DF decided that's not what his life should be like ( he was planning on telling her it wasn't working etc) she told him that she was pregnant (after telling him she couldn't have children due to medical conditions and that she was on the pill too), please don't get me wrong he loves his son so much as he does all his kids but he had told her he wanted to wait if he was going to have more kids.
He stuck with her until his baby was born and decided that raising a child in such a hostile and unloving environment was not right so he moved out (but still supports his son and wants to be in his life). Ever since them she has made his life hell, she suffers from 'chronic fatigue' ( I'm aware this is actually a condition and I have a lot of sympathy for people who actually suffer it but if you can go to the gym three nights a week, the pub at least twice a week and work as a babysitter a few days a week without the government knowing -she's on a disability pensions for this 'condition' - all the while her own son is in daycare 4 days a week, then is reasonable to say that you probably don't have CFS).
She is constantly telling my DF that he is a terrible father, he's not capable of taking care of HER son, he has no idea what he's doing and he only cares about his 'new' family ( meaning my family who have welcomes him with open arms) I guess my point is she comes across as very jealous of our new life together (she had their wedding planned before his son was born) she thinks I'm getting everything that was hers (wedding, a child, a loving and supporting partner) in a way she thinks I stole these things from her - my DF met two hours from where we live now as he had moved for work, we only moved back so that he could see his son more (which he took a pay cut to do).

I really feel sorry for her, for the fact she can't move on, for the fact she has to drag my DF through hoops to see his son and for the fact she is dragging her son through all of this too.