They're still together now.
There has been no breakup. Superman and Diana are still dating in Justice League. Johns just isn't wasting page space showing the two of them kissing every single issue.
The only thing that has changed is Johns just woke up one morning and decided to start writing Diana the way he should've been writing her from Day One.
Stopping the villain prevents the villain from hurting anyone else. Once the villain is defeated, THEN she can focus on helping the people he has already hurt.
That's the DEFINITION of caring about people in trouble. Stopping the thing that's hurting them so that you can help them recover. If you focus on saving every person in danger, then while you're doing that, the villain is moving on and hurting more people.
That's not "coincidence." That's called a "plan." A plan with "Help People" written all over it.
Nope.
No needless violence at all, other than the attack on the naval ship, and even that was a measured response. She could've sunk the ship if she wanted to. Instead, she just attacked it's guns.
Every other time, Diana was in control and did nothing that was unnecessarily violent. She even tried to calm down Superdoom, you may recall.