From what I understand, Heard is alleging he's abusive after drinking or using drugs. So it's possible these problems are more recent and didn't affect his past relationships. With Paradis, especially, he had two children, so there would have been a reason for him to more consciously abstain from both of the above. Whereas, with Heard, he was suddenly with a younger person and child free (a good deal of the time), so possibly more likely to indulge.
Obviously, we don't know what really happened yet, but having the support of two of his exes, doesn't clear him.
Obviously, we don't know what really happened yet, but having the support of two of his exes, doesn't clear him.