trompait

/tʁɔ̃.pɛ/tromper
1.
verbInd1stImparfaitSing3

was cheating on (a partner)

was deceiving / was misleading (someone)

Il trompait sa compagne depuis six mois avant qu'elle ne s'en aperçoive.

He had been cheating on his partner for six months before she noticed.

2.
verbInd1stImparfaitSing3

was mistaken

was wrong

Je pensais qu'il avait raison, mais il se trompait complètement.

I thought he was right, but he was completely wrong.