OP, you are not a mug, please do not think that you are. You went in to a relationship with honest intentions and have done your best by someone you care for, unfortunately it just not has been reciprocated. None of us have a full insight in to your relationship, you know it better than any of us, but from the little you have said, this man does not sound pleasant. He does not sound like one who will look after you and your children and consider them like his own one day. He obviously does not see the relationship as equals either. You do not deserve that.
You have a roof over your head, are not dependent on anyone and are providing for your children, you have a lot to show for what you're doing. Don't take away your hard work from yourself.
Go on this holiday, consider it the breaking up holiday, enjoy it best you can and certainly let the children enjoy it. Perhaps before you even consider ending the relationship, speak to him about the relationship status and whether he will begin to pay half the rent and put some money towards the bills as an equal partner that wants a future with you. If he says he cannot then it's from then you can start your process and tell him that this is not the future you want.
Find some solace in friends and use them for support, you do deserve better, whether it be from him stepping up or with someone else entirely, just do not sell you and your kids short. They deserve someone who will love them too.
I wish you so much happiness OP and hope things do get better for you, if you ever need to talk, never hesitate to reach out to me on here and others and those around you. Don't let yourself feel isolated.