I don’t want him anymore. But I also don’t want him to ever be happy with anyone else… I’m not sure what to do with these truths?

Those sound like two fine feelings to respect and accept. They are both true. You feel those ways. Now... Next step is to just let them be and move onto something else.

People don't have to act on every feeling and the ones that are persistent, to not act on them is extremely difficult. Otherwise the world would have no addicts, stalkers or anxious people.

Its hard but completely possible to live freely imo.