You can make the spell yourself. I'm a rune and crystals person myself. You need to find out what kind of magic you prefer to use. Maybe you like word spells that you just repeat - rhymes or something, or maybe you want hoodoo or herb or candle magic, or tarot cards by invoking their magic and not using them for divination - people do that but it's not my thing so I can only suggest runes - my thing, or crystals. Mind magic - getting a mental wavelength relationship is also something I would start if I wanted to create a strong relationship which absolutely works with making someone want to be with you. - that freaks people out so may not be your thing.
So the others tried to warn you but didn't offer anything. It usually is best to break off an attachment that hasn't worked and for that try chrysophrase - the crystal to mend a broken heart. I've never found cord cutting spells to work but others do. A bit of Buddhism is also nice because you mediate and try to let go. Google spells and you'll find plenty to try to break of a relationship - in the flavor of the magic you prefer to use. See my first paragraph.
You can remove the guy pretty easily but lets not forget there is karma with what you do so make sure you're doing the right thing with good intent and not completely self serving which will literally cause you to sabotage yourself. I would use Isa and that would remove him for a few weeks to a few months before you have to invoke it again. But there are many things you can do and it's possible you remove him from your life and not hers. I wouldn't find it a problem removing him because I've done it so much. Putting his name on a piece of paper, drawing the isa sign - a line - through it and intensly invoking isa at the same time has always worked for me as imagining the person and drawing the line in the air down them while invoking isa with your intent works too. I sadly got rid of a problem neighbor by doing that and forgetting how well it works. She instantly disappeared from my life, my families life and physically from the neighborhood and I recently found out I hadn't seen her since I invoked ISA because she was going through a separation and will likely have a divorce. I've only used that rune - which is over kill, for people there is no chance in everyday life that you can remove them if you don't use it. Ie a co worker who sits next to you. It works like a charm, within a few days you don't see the person again for months until you re-invoke it. It's worked everytime for me. I am dealing with a very real suspicion that I broke up a marriage by invoking it to get rid of her which does bother me so I'm not using it again on her and she is coming around now - while I have still not seen her. They will repair their marriage on their own and apparently are.
That said, you have kids and you can choose to try to get her back - which I cannot call whether is wise or unwise because I don't know your situation.
What I would do first dispell negativity, - many ways to do this - invoke the rune dagaz on you and her, hold obsidian to get it off you, etc. You can google runes used for attraction, I would probably start with Wunjo to put glamours on me - ie for people to want me around. Essence glamours tend to work well with me - I find them more powerful than say trying to glamour yourself to physically look better to people - which incidentally works too. How they feel about you is more important is all I'm saying.