This is the only Manhwa where I somewhat agree with the review of @Myriadofhate ~
Season 01 - 6.5/10
Female Lead is the epitome of Rookie behaviour. Her mission takes a backseat most of the time and Her feelings are a top priority for her. She constantly tells ML how she is smitten with him and as a spy, she almost blows her cover almost within a day of meeting the Target. She gets to enter the House of 2nd ML (Target) but never tries to put a listening bug in his House. One of ML's colleagues tells ML that he should stop acting like a proper Spy, give some thought to their fake Marriage and try to understand FL's feelings. At one point, the Male Lead becomes stupid and acts naively around FL as he tries not to feel jealous of FL reaching out to 2nd ML. Also, as ML decides it's time to face his feelings Female Lead decides that she needs to stop being childish as she catches on 2nd ML's feelings and starts drawing a line between ML and herself.
Meanwhile, 2nd ML keeps overstepping the boundaries even when FL has been constantly telling him that she loves ML and she is a married woman (even if it's a contract Marriage)~
Chapter 50+ - 8.5/10
FL's communication has been her strong point in All 50 Chapters before and continues to get better. She encourages ML to even propose to her and she won't have a 'No' for it. She also puts clear boundaries between her & 2nd ML about how she feels about him - at one point she compares him to a puppy and all she feels for him is Pity..
Once ML accepts his feelings for FL - He becomes a great Listener, almost a strong support (that's what he was sent to do) and stops feeling Jealous, rather he lets FL decide their fate. By the end of Chapter 52, He turns into a great husband material~
2nd ML I don't know how to describe him. He is an attention seeker, spoiled, bratty & lonely Kid with lots of money who hasn't grown yet. As an adult, I don't see him as an adult at all. His sob-story is convoluted too. His borderline stalking, almost kidnapping and random spying on the FL & ML convo makes me feel ICKY. He gets the Not-CREEPY pass just because he is Handsome.
Then, there is 2nd FL, the Woman who is way better than FL for 2nd ML. She dedicates herself to 2nd ML and fights a Lonely battle for him.