The fact that he has a motivation to figure out what’s happening with Philip can work against him, as he obviously isn’t happy that the woman he loves moved on to seemingly agree to marry a guy she hasn’t known all that long.
Natalie isn’t unreasonable to assume that his actions to try and figure out what happened with Philip are because of their personal relationship.
That said, “In the Valley of the Shadows” proved that Will might not be the best placed to help reveal the truth to Natalie.