I've watched many bl drama, but this one is really on another level. The first season was already great and cute, the characters were really well written, they have their virtues, they have their flaws. Flaws that appear at top energy in season 2, because it's easy to get together with a lover, it's hard to mantain a relationship.

Seo Joon and Ji Woo love each other and try their best for their partner in their own ways. Seo Joon is often busy with his job, he's wanted by everyone, surrounded by all sorts of people, from fans, to co-workers. He still does his best to go home to his lover and spend as much time with him as possible. Ji Woo, on the other hand, is alone, literally, even in season 1. His only "friend" was the owner of the restaurant who tried to trick him and now at the beginning of season 2, the only person close to Ji Woo is Seo Joon. This situation is too heavy on Ji Woo, for him, his lover is everything, while Seo Joon meets all sorts of people. Ji woo's frustration grows even if he knows that Seo Joon did nothing wrong at all, his low self-esteem makes him think he's just one of the many people in Seo Joon's life, he will soon forget about him anyway so he chooses to disappear from his life.
At first I couldn't understand Ji Woo's choice, but after the end of the season I was able to understand why he did what he did. Ji Woo moves to his native village, where he finds an old friend with her daughter and has also the chance to meet with his ex-girlfriend. Finally, Ji Woo has a background, friends around him and his own restaurant and even if things don't work perfectly (his restaurant is always empty, he doesn't have a great relationship with most of the people of his village) we can finally see Ji Woo as a character, with his own story, disjuncted from Seo Joon.
While Ji Woo builds his new life, Seo Joon is left confused, with no clue and with no explanation. Eventually he manages to find Ji Woo and he tries his best to get closer to him again. Seo Joon befriends the people of the village and with several excuses he's often there.
We also meet Ji Woo's ex to add a bit more of drama (as if Ji Woo himself wasn't enough), she is still in love with him and in the past she left Ji Woo all of a sudden to study in America. She basically did what Ji Woo is currently doing to Seo Joon. She had her own issues, her own weakness and she felt her boyfriend didn't care enough about her. It is the kind of behaviour that can seem extremely selfish, but sadly it happens when we are in a negative moment. Her presence helped a lot to put some order in many characters: Seo Joon misunderstands a conversation and believes Ji Woo still likes her and decides to give up on him, Ji Woo on the contrary starts to think more carefully about his situation with Seo Joon. So yes, now it's the time to turn the table and it's Ji Woo who (after some other events) understands that he wants to go back to Seo Joon.
Seo Joon doesn't make much resistance because he's a big simp, so 9 episodes of angst are solved relatively fast once Ji Woo explains him what went through his mind. And I'd say that also the audience understands him and forgives him pretty quickly, at least I did. His best ability is to build walls around himself (as Seo Joon himself mentioned in season 1) and this time he just chose to build higher and thicker walls, to protect himself and his lover from his own dark feelings. And Seo Joon is the only one stubborn (or crazy) enough to crash against those walls to the point of hurting himself. But eventually he managed to break them.

For half of the season, Ji Woo's behaviour was a complete mystery, just like it was a mystery to Seo Joon. In some parts, he is almost cruel in his attempts to push Seo Joon away. And I personally believe that breaking up without giving a real reason is really immature. But I can see what the author wanted to do with Ji Woo. He was pretty confused by his own feelings, he felt lonely, he felt gulty for feeling jealous of his boyfriend. His low self-esteem and the idea that he didn't count much in Seo Joon's star life did the rest. His biggest limitation was, in season 1 like in season 2, his inability to communicate properly. Ji Woo's negative feelings grew so much because he never expressed them. "I have such a great boyfriend while I feel like a piece of trash", what can you even do in this situation? What can Seo Joon do more for him, even though he's already been perfect? This was probably what was going on in his mind, so he chose to leave.
Leaving was probably very good though because not only he found friends, but also because it allowed him to face properly his problems and even have the first fight with Seo Joon.
The feeling is that after this big crisis they can now have a more balanced relationship. Ji Woo has learnt to be more open and honest, Seo Joon has learnt more about Ji Woo.
Ji Woo doesn't wait lonely anymore for Seo Joon to come back, he has his own restaurant, he didn't run back to Seoul, but they try to meet as often as possible, if Seo Joon is free he goes to Ji Woo's village, otherwise it's Ji Woo who goes to Seoul. They are two individuals who chose to share a path together, they're not a couple that has to be tied at all costs to the point they lose awarness of who they are.

Kudos to the way the first episodes in particular were handled. Flashbacks overlapped with the present time, for example Seo Joon goes back home and Ji Woo is there, but it's only a memory, he's actually alone, adding to the confusion regarding Ji Woo's choice. The overlaps happens also while Seo Joon is acting in his drama. Fantastic the scene when he floods Ji Woo with calls to meet him and the scene moves to him on set, shooting a scene of a character making a phone and saying to have some pride and not call so often.
Kudos also to the side characters who weren't just npc rooting for the mc, but people with actual stories. Pyl Hyun is just amazing, this guy makes me laugh so much, as well as the poor manager who has to handle Seo Joon's (and Pyl Hyun and Ji Woo's) personality. Ji Woo's neighbour and her daughter were also nice characters who got some background on their stories, as well as his ex-girlfriend.

BL are usually stuck in overly cute and fairy plots, To My Star on the contrary manages to give some realism, as painful as it is.
Let me finish this very long wall of text by expressing how much I love Seo Joon. He isn't perfect, but god he's so genuine, cute, and honest that it is literally impossible not to fall in love with him (only Ji Woo could resist this much lol). It's been a while since I've last felt such an affection toward a character in a drama.