My ex left us in the most damaging (to our then 3.5 year old son) way possible. He took DS off for the day, having been - I thought - at his parents, having been helping them out with landscaping their garden, the previous night. All well and good. DD (then 11 and from a previous relationship, but ex had been in her life since birth, pretty much, as we've known one another since we were 11) and I were planning on spending the day sorting her bedroom out. Ex called me 10 minutes after he and DS had left to tell me that his girlfriend (whom I knew nothing about) had given birth to their child the previous day and he was taking our DS to meet "his new sister". He then hung up and no one would answer any calls. His parents, when I went there - actually to bring my DS home - wouldn't answer the door. I didn't even know if DS would be brought back to me, or if ex had decided that he and the girlfriend (now his wife) were going to play Happy Families...
DS asked him why he left us a few weeks ago, actually. Following DD (now 19) having a breakdown and a lot of emotion coming out about her having "been abandoned" - or maybe rejected - by both her biological father and the man she considered her Dad. I didn't know DS was going to ask, but... well, he knew about the girlfriend before I did. He kept telling me about "Daddy's friend, X" and, when I asked about her, his "daddy" said, in front of DS, then not even 3, that he was a liar and "just trying to cause trouble". Ex's answer?
Because he didn't want to be tied down to us and X was "more fun" than me.
What I haven't told either one of the children is that ex took a lot of drugs, and I refused to - hence being less "fun" than X... who is now shackled to a permanent man-child, with two children by him. She's also, according to mutual friends, no longer "fun" in his eyes. Oddly enough, when you're a responsible mother... you do cease to be "fun" in many ways. Sadly, a lot of men, including my ex, don't ever grow up mentally or emotionally. Physically, they may be adults - but that's about it. I suspect this is, in many cases, encouraged by their parents.
My ex is supposed to see DS (he won't see DD, for various reasons, which I do actually understand - but will never forgive him for) every other week. But, very often, he disappears off on holidays abroad with X and their children - and we know nothing about it until his mother arrives to collect DS to spend time with them (which I have no problem with... except for how abandoned and unimportant it makes DS feel). Actually, though, I've not seen my ex since his youngest child was born 4 years ago. I know a lot of people encourage co-parenting, and being friends with the other parent who is no longer with them, for the children's sake... but ex was my best friend from the time we were 11 years old to the time we were 31. It's better for my children if we don't meet. Because I don't know that it'd end so very well if we did. The lack of consideration for anyone's feelings except his own is horrific - and, sadly, something which I think is firmly cemented in a person by the time they start school. Ex's parents didn't raise him (he's their PFB, and was actually raised by his maternal grandmother until he was 6, then briefly sent to boarding school. The two children that his parents did raise... well, they're emotionally mature/stable!). But his leaving has had knock on effects. My DD tends to date boys/young men with issues similar to her own, and I suspect this is because of the way in which she was abandoned by both her biological father (who hasn't seen her since she was 3 weeks old, was abusive beyond belief, and she truly is better off without him in her life - although, to be honest, I don't think she grasps that!) and by my (actually emotionally abusive, but it took me until very recently to understand this) ex. Unfortunately for my ex, our DS resents him because of how he refuses to even acknowledge DD - but DS doesn't know the reasons, and... well; I don't think it would help if he did know. It might destroy his relationship with his sister, if he did (and yes: I know that she's not to blame for ex leaving, but one of the reasons as to why he won't acknowledge DD in any way, is because she lied about him physically abusing her - in full sight of me, incidentally, which is how I know she lied. I would have chosen her/DS over ex any day of the week, without hesitation, but I also know that her issues concerning her biological paternal side were pushing her to force both myself and ex to choose her. I did, he ran for the hills, so to speak!).
But... like many other mothers out there, it's me left picking up the pieces of this situation - and I'll be doing that, I suspect, for the rest of my life. DS remembers only too well going to see his prematurely born younger sister in the hospital - and has developed a phobia about hospitals as a direct result (not great, considering that he's required a lot of surgery and medical interventions over the years!). He remembers, too, the way in which he was encouraged for years to call X "mummy", and how confused he was when they eventually married (he asked if I was still going to be his mummy when his daddy married X, and if DD was still his sister, because he had "another sister now"). I cannot do anything to change that. I don't know if he remembers his father calling him a liar to his face. I truly, genuinely, hope that he doesn't. Both of my children are very fortunate that my ex has a brilliant younger brother and sister - who have always been there for them. Even though they're both married with children of their own now, they spend time with both DS and DD, they make sure they know how loved they both are by them, and... I don't understand how ex could be so very different to his own siblings. But I'm grateful that they are. DD, for example, is Godmother to the younger brother's eldest daughter and she has a fantastic aunt/niece relationship with the brother's wife.
Just make sure that your DC know how much you love them, don't speak ill of their father in front of them (something which I have never, and will never do - even when faced with my DS asking me why he "had" to call X "mummy" and if I'd still be his mummy when ex and X married), and understand that this isn't your fault, or your DC's fault.
It's his.
And it'll be his loss as they grow up to be fantastic individuals - because of you and your influence.
(I would, however, encourage you to find someone whom your DD can talk to about how she feels concerning this situation - if only because I truly wish I'd done the same for my DD. Bottling up, or repressing her emotions concerning her dad leaving... please believe me: I'd not wish a breakdown like that which my DD's had, on anyone. And it was, in part, because of my ex - who was her "dad" in every way but biologically, for 11 years - abandoning her.)