Geez, Sim, I never thought I'd say this, but poor XH! It's kind of coming together how he could have the issues he has! Of course, that's not an excuse, just a reason to do something about it. Well, go XH for putting a stop to it by ceasing communications. Do you think it could work for you two to carry on this unpatented business together? I reckon you should go and patent it under your name and let XH in on it unless his behaviour deteriorates. XFIL's behaviour really does paint a better picture of XH's background - he couldn't have been a very happy kid with a father like that I can also see why he is actually working hard to have the kids think well of him. *****, it's so sad, I actually feel a bit sorry for your XH, especially if he can't bring himself to work on the issues he has inherited (anger management, insecurity etc).
Anyway, Sim, you are such a tough cookie - you're gonna make it past this
ETA: can I stress this enough - I don't feel sorry enough for him to think that you should take him back! He has way too much baggage that he tries to get you to carry on his behalf for that to be a fair situation for you and the kids!