WAIT... IT DOES MAKE SENSE, BUT AT THE SAME TIME IT DOESN'T... JAY WAS ADMITTED TO MILITARY, RIGHT? SO, I GUESS THE PRESENT TIMELINE WAS BASED ON THE MANIPULATED PAST AND THE FUTURE TIMELINE STOPPED IN JI YUL REMEMBERING THEIR PAST (PHONE CALL WITH HIS MOM & AT THE HOSPITAL)
So in summary
The present (ending) was based from the past where byul came and suho saved rose. While in the future rose is dead, jay is in the military, byul doesn't remember his hyung and hyul remember their past + is in the hospital
The thing is you can't do roleplay if you don't trust your partner in a certain extent. That's why I think their relationship is healthy and they have a deeper connection. They're so adorable ┗( T﹏T )┛