Broke up with him maybe? Like pushing MC away when he went back after getting discharged from the hospital then knowing the boyfriend you thoughtwill always be there for you already got someone else while you're coming back from the brink of death.
Personally, I think Taejuu is also a victim. This is literally no ones fault. Taeujuu was hearbroken and grieving MC's assumed death, he regretted not begging the MC so that he won't go and risk himself for the thing MC love to do the most. He cried and grieved for more than 3 yrs, after a few years he believed that MC died. He found another because of the comfort that person gave him when he was grieving, but he was also decieved by that same person. Manipulated into thinking that he forced himself to him, making him feel guilty and responsible for that person, when in fact it was consensual and not forced at all. Because of that relationship, MC who he loves the most, was pushed away. Nah, i'll stop there. This is really tear jerking. But also lovely.
I know what the ex did was wrong and I will never justify what he did but in the end he realises his mistakes and does wishes mc's happiness....so I really do hope he will get a happy ending too.