Accurate, which this isn’t for Marianne (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

FAITHFUL (probably a reference to the singer Marianne FAITHFUL [1946-2025] who may not always have been [which this isn’t] FAITHFUL to her husbands.  Alternatively, a reference to the character MARIANNE Sheridan in the 2020 TV drama Normal People)