Do you have any advise. I've been alone for over 18 years now, so I should know. Ulimately you will face the situation and you will be strong enough to get through. Threatening to leave and getting angry are different stories altogether. Emotional blackmail is just a way to avoid communication and try to control the other person unfairly.
Anger is another way to avoid communication and try to control the other person unfairly.
Try to get him to join you in relationship therapy. If he's not interested go see someone on your own. Also I think you should take steps to make sure things will be ok for you and your kids if he doesn't return. I hope it does work out, but like many people you need to work on building your relationship and opening up the lines of communication. Regardless, start accepting that you are strong and competent and that you and your kids will be ok.