I think you've forgotten that the ml knows mc's soul is his former boss'. Ml is acting like this because he knows his boss is inside the idol's body hence ml's feelings are towards the soul, not the body. Before the crash, they've known and was beside each other's side for years. U pointing out the gap of their proximity after the "ml knows its impossible but his boss' soul is in that body" realization doesnt compare to the years they were together before. If u know a person for 80% his life, months of separation dont remove feelings unless its negative. Ml doesnt have negative feelings for his boss.
The romance just feels so out of place and random...the mc and ml haven't spoken to each other in like 30 chaps b4 this and they hadn't seen each other in person in like 60. Them meeting and the ml having all these strong feelings for him just feels so random rn.