how do you bind someone from giving someone else a love spell?

Here is my question: what is the intent of your spell? Is it for personal gain? Binding spells have a nasty habit of kicking back into the rule of three (what you send out comes back to you times three). He is a big boy. He is, presumably, capable of protecting himself against a wily witch. Please, think about why it is that you (collectively) feel the need to treat him like a child. If it is for 'his own good' aren't you depriving him of his free will? Instead of binding her, please just do a free will spell.

I don't personally believe in spells, so I don't think that it'll work but only time will tell.

Talk to her rationally. He has a child! Does she want to break the mother's heart and the child's heart by 'stealing' her ex-boyfriend back? There was a reason the ex was put there, so remind her about that. If he's the one that doesn't want to be with her then explain that she doesn't want to be with someone that doesn't TRULY want to be with them. She doesn't need spells to find her true love - she just needs to look harder.

I'd talk to him and ask to do a protection spell for him.

Have him sprinkle salt on her doorstep, she can cast no spell of harm to him until all the grains have been counted.

I don't believe in love spells.

burn a white candle and sage for purification. say his name three times and say i protect you now and always from unwanted influences in your life. so mote it be.

Drop a 4 way hit of sunshine, go skydiving.

Ask the Lord Jesus Christ to cover you with His blood and His protection.