credit to @gm4queen (forum soompi)

This picture at the beginning of each episode doesn’t just represent the title of this drama. To me, it also gives us clues about the story. The blossoming tree, a cherry tree, embodies the blossoming love between our leads, JH and JI because the cherry blossom is often a symbol of love and passion. We often see in K-dramas scenes where the main couple walks under cherry trees in bloom reinforcing the idea that this couple is fated to be together.
Besides this picture not only marks the start of their love, it is also illustrating that their love is bringing new sides of our characters. JI is changing, even her friend noticed that she smiles more and is more creative thanks to her new feelings. It was as if JI has come back to life and before, she was like hibernating. She was not really herself in reality but she had no idea. It is the same for JH who was so traumatized that he only worked and played basket ball during his spare time. Now, for the first time he started flirting with JI, he is definitely more active.
Finally, since their love is connected to a season, the spring, I would say that their love is natural and it can not be controlled by humans and society. That’s why neither JI nor JH can control their emotions and their mutual attraction.
GS won’t be able to stop it… His fight will be pointless, nevertheless he has no idea about it.
The second aspect in this picture is the moon. I have the impression that their love is also very discreet and even secret because of the presence of the moon, since forbidden lovers usually meet during the night. I am not saying that their love is forbidden, far from it, it is just that it will grow unnoticed by the others. Notice that until now, no one is aware of their connection. Sure, in the next episode, her friend will see JI with JH, yet I am quite sure that JI will never tell her what really happened between her and JH. JI has no idea what she is feeling right now.
Notice that they often meet during the night, like for example in this scene: (cr. to @Pmyonly, forum soompi)
This gives the impression that they are secret lovers… but they are not. The night is the only moment where they can talk to each other without getting noticed. Furthermore, since I have started watching K-dramas, I have noticed that we often see a scene where the FL and ML are together while it is snowing. The reason is simple: there is this belief in South Korea that if you are out in the first snowfall of the year with someone you like, true love will blossom between you. In the drama, the characters (f. ex. JI’s sister) mentioned that this could be the last snow of the year, hence we could think that this scene has not the same meaning. Yet, I doubt it.
For me, this scene underlines one more time how natural their “attraction” to each other is. This scene indicates that they are fated to be together, this will be true love. Furthermore in my opinion it doesn’t even matter if it is the last snow or not, the most important aspect is that we shouldn’t forget that both protagonists have been hibernating so far, hence this explains why they couldn’t meet in the first snowfall, they are late because of their past. The “last snow” marks the start of their blooming love. Moreover, the spring symbolizes birth hence everything is new to JI that’s why she can not clearly recognize her feelings.
In the last scene of the episode 4, the viewer can see another illustration of the title:

Above her head, you can see the reflection of the blooming cherry tree, an indication that her heart has been moved. So the director is linking this scene to the first picture shown above. In that scene, we shouldn’t forget that she is actually admitting herself to JH that she is so glad that she got to know him. In this confession, she definitely uses the expression “I like”. This was a huge step for her and gives “hope” for JH. That’s why he admits that he has bad desires. Here again, he clearly reveals that he wants more.
Anyway, this taking is important because, like I had mentioned, this tree symbolizes the return of life and a change in JI’s heart. When JI was driving with GS, we never saw the blooming cherry tree. She is getting closer to her inner feelings.
I sense that she is reluctant to give in because she still perceives GS as a good man and doesn’t want to be the bad person: if she broke up with him, she would betray him. However, her judgement of GS will change next week because she will realize that GS is quite manipulative. Notice that in the preview, GS’s words seem to indicate that she is the bad one, making her feel guilty because she doesn’t want to get married. I sense that at some point she will get aware that GS has been trying to make her and JH feel guilty and bad all the time, while in reality he was never a good man from the start.