While I think that your fella has got quite a few things wrong, I fear that you are perhaps expecting more from him than you are going to get, especially if you refuse to see his children or have them over again.

Whereas I understand having the children with you nearly every time you see him is too much, and that it is too early in the relationship for that, I think a blanket ban on seeing them is not the way to go either. They are part of him, you can't reasonably expect to change that, nor should you ask him to choose or put you first. Make him chose and you will lose. I am actually concerned too that they were introduced to you so soon - 5 months of dating should really be where things are still uncertain.

In an ideal world, if your relationship is going to last in a healthy way, he will let you have some input in their lives, and see that you actually would want the best for them (and that want to be genuine). That includes being strict at times and insisting on house rules - with the back up of your fella. However, in turn you will have to accept that they are the most important part of you boyfriends life, and instead of being threatened by them, you should enjoy them and be doing your best to build up a little tight unit - an extended family. That also includes putting them before you on more than one occasion. Anything less is not fair on them. They need security, and not to made to feel unwanted by you, no matter how much that may be true.

I think tho, you may have to accept that - in your own words - children are a 'deal breaker' for you. There's nothing wrong with that, truly there isn't. Children are not for everyone, you've had all these years without them, building up your life, house, fancy cars etc, but to ignore that gut feeling and making ultimatums or banning kids from your life isn't the way to be in a good, healthy and successful relationship, no matter how much you both love each other. Sometimes love just isn't enough to overcome circumstances.

Good luck.