When a devoted woman suspects infidelity in her husband, her investigations leads her to discover unforgiving facts about him which may force her to take an irrational decision with daring consequences.

This logline is quite vague.

"Unforgiving facts," "an irrational decision" and "daring consequences"...
None of these actually give us much to work with.

All we REALLY know is that this movie is about a woman following her husband.

Make it clear why this will be an exciting movie. What are the stakes? Because of the infidelity, we already assume she might lose her husband. But what else will be at stake? Tell us in the logline.

Also, what does she learn in the process. She is 'devoted', which is not necessarily a weakness. Is she also gullible and naive perhaps? It would help the logline if we can see some character growth for the hero.