If someones personality changes when inebriated, and they are always inebriated, than that is who they really are.
It doesn’t matter if they are ‘nice’ when sober, if they are rarely sober.
A violent drunk is an abuser that sometimes sobers up. A catatonic addict is an emotionally neglectful parent that some times sobers up.
I have learnt to view people based on how they are treating me, not based on how they are when sober or mentally healthy - this has enabled me to see (and end) toxic relationships before I am was further hurt by them and their abusiveness.