You probably wouldn?t feel so strongly about the disparity in earnings if the situation wasn?t so extreme. If the maintenance payments weren?t so disproportionate, and if there weren?t frequent foreign trips to finance, then I doubt it would all be so galling.
Oddly enough, your redundancy might be a blessing in disguise, because it will surely force him into facing reality? It?s probably very easy to spend all his money on the ex and DSS, when he knows that you?ll pay for everything else. But once your salary is no longer there, SURELY he wouldn?t blow it all on DSS leaving you and the children with literally no food on the table??
Rather like I don?t panic if I?m running a little short at the end of the month, because I know DH will ?top me up?, but if I couldn?t rely on that, then I wouldn?t dare run short, because I?d know that no further funds would be available?
Does he base his maintenance payments on HIS salary, or on the joint household income (which he shouldn?t do) or does he pay what the ex demands? If it?s anything other than the first option, then this HAS to change. DSS is NOT your financial responsibility. Particularly not when you?ve already got one child with two more on the way.
I do wonder if it?s ended up like this because (a) he?s been allowed to create this situation; or (b) he?s one of these men who?ll do ANYTHING to avoid conflict with the ex? If it?s primarily the latter, then I think you?re in for some challenging times because he may play the ?if I don?t pay up, then I won?t get to see DSS, and do you want to be responsible for that?? card. You and I call it emotional blackmail, but if he?s terrified (or if he pretends to be terrified) of upsetting the ex, then he?ll probably dig his heels in.
I think your best course of action is to present the figures simply, in black and white, and ask him to work out a solution with you. Unfortunately, if it means he has to curtail his foreign trips slightly, then so be it. You?re not trying to stop him from seeing his son, but you?re not responsible for funding the flights, nor are you (I assume?) responsible for DSS and him living in different countries. How did that happen by the way? You can?t deny your three children the basics, ie new shoes, to facilitate his rather extreme access situation.