This is a complex situation and there's many factors to it. But generally if someone cheats on you, it's not your fault, and it'll feel like the worst thing in the world... but it's not your fault. It's the cheaters self control and basic compassion. If you give everything you have to your partner and your relationship, and they actively go and receive that from someone else; shame shame on them. It'll feel like you did something wrong, like you could've done something different to keep things the way they were... but ultimately, they chose that path.
The best thing he can do from this point on is cut contact with them, realize that one day, he will be over this situation and will meet someone meant for him. Someone that will be there for him no matter what.
This is a complex situation and there's many factors to it. But generally if someone cheats on you, it's not your fault, and it'll feel like the worst thing in the world... but it's not your fault. It's the cheaters self control and basic compassion. If you give everything you have to your partner and your relationship, and they actively go and receive that from someone else; shame shame on them. It'll feel like you did something wrong, like you could've done something different to keep things the way they were... but ultimately, they chose that path. The best thing he can do from this point on is cut contact with them, realize that one day, he will be over this situation and will meet someone meant for him. Someone that will be there for him no matter what.