I'm slightly meddling with my ex's current relationship.
How are you meddling with my ex's current relationship?
I try to encourage others to breakup with her by saying things like "she'll mistreat you etc"
It's not nice to try and break up a couple. You should just mind your own business.
He's better than my ex so he should be with me not her.
You don't have any say in their relationship, if they found out what you're trying to do here they'll keep you at distance. You should get over your ex and move on.