I think you need to be aware that the award of spousal maintenance through the court system isn't particularly common. The odds on you having received maintenance for YOU were therefore low unless your ex is a particularly high earner (and this would mean, usually, him earning well in excess of £2k a month after deductions, not before). And it doesn't help to say it, I know, but if you wanted the protection of marriage, you really should have got married or entered into a civil partnership if you have some kind of objection to marriage.
There is an expectation that an adult makes their own way in life if a relationship breaks down and that includes where there are children involved. It can be quite hard to get your head round this kind of thing but it is not your ex's responsibility to provide for you. You will receive the same child maintenance as you would had you been married. Your children are not worth less in this respect.
You seem to be advocating that father's shouldn't have the right to a relationship with their children unless the mother says so, unless a wedding took place. You need to think very, very carefully about this. Your children have a right to a relationship with their father, no matter how badly he may have treated you. He remains their father and there is nothing at all you can do about that. Developing a positive parenting relationship with him is key if your children are to grow up with him in their lives and are not to be screwed up by what has happened. Way too many parents - of both sexes - get caught up in hating the ex so much they can't see the damage it causes to your children. Someone told me when my ex walked out on me (I too got an e-mail) that I had to allow my children to love their dad, regardless. Try and be the bigger person - it's very, very hard!
I am sorry this has happened to you. Please know that from the depths of despair, it is possible to recover and go on to bigger and better things. My life has changed beyond recognition since my ex walked out but I wouldn't have it any other way now - I have a new home, a new career, new friends and am getting along great. It took a long time but I got there. You will too xxx