Neighbours is set in its own fictional universe so I don't apply my real life standards to it. I think Paul is a great character because he's entertaining and charismatic and played by a good actor, however I'd despise him for his immorality in real life. I'd also tell Terese to run a mile from the scumbag, but I like their on screen chemistry and want to see them get together.
As for what Paul has done to Terese personally, I don't think that matters. He's a very bad person and would do the same or worse if he thought someone had killed one of his kids - so he's a hypocrite for blaming Terese. Plus he has in fact hurt her personally. Remember that time not so long ago that he planted drugs on Josh with the intention of sending him to prison? If I remember correctly, Josh only escaped punishment because Naomi discovered Paul's evil plan.