I truly feel for you, a very difficult time as with all of us on here but look at yourself. You are making a go at bettering your future through your training whilst looking after a very small child, you should be commended for it.
DR'ing would suggest that you need to make a decision here, is he having an A? If so there needs to be lines drawn - end the A or move out. You need to protect you for your own sanity and those of the children. If he isn't then great! Ask him to move to his parents for a while and let him stew, go dark no texts, emails or phone calls except the obvious.
Pursuing people like these tend to push them further away, really I know it's not what you want to do BUT not having contact works in your favour they start to think about the sitch and get in contact I've experienced it many times but remember it's a rollercoaster of a ride - ups and downs prepare for it. Whilst you are away from the problem you can then work on yourself with a clearer head and start to prioritise the things you have going on and better choose what to drop to make your hectic life that much easier.
What can you control? I know separation is the last thing we should do but sometimes it benefits! He has all the power and is dictating how this is being played out, you're better than that. Giving an ultimatum about his attitude towards you and his family with the above conditions might actually wake him up and show him you mean business - you regain the power here. Mention to him you L him and you want nothing more than the M to continue then hit him with the 2 conditions, he may say thank you and move out prepare for it BUT am I wrong in thinking this is what he wants anyway..?
Please I'm the last person to give advice I'm separated from my WW but it has given me greater control over me and my 2 boys. I am DR'ing and if you haven't got the book GET IT. To me it looks like you don't know whether your coming or going this needs to stop you need to regain control of YOUR life and not let him dictate how your going to live, that's not fair and it's not right.
Look into the LRT and give this patience and time but gain control first you need to be the one driving your life not him and with the right things in place who knows what will happen.
Be strong be patient and look after yourself.
Mark.
DR'ing started March 2017
Don't blow the last bridge up from fantasy island, act "as if".