I don't think Masaki and Sohta had a good start to their relationship (blackmail is never a good start to anything, honestly), but at the same time, if you decide to commit to being in a relationship with someone, there are some basic courtesies you owe the other person. For example, honoring requests that are not difficult shows you respect and care about the other person. Not being alone with someone your partner has told you makes them uneasy, even if you don't believe them, is not a difficult request. On top of that, Masaki was going to let the nurse have his way with him but stopped him because the room was dirty???? He had the ability to get out of the situation and did it because the room was dirty, not because he'd be betraying Sohta??? Sorry, but even I can't follow that trail of yaoi logic.
I don't think Masaki and Sohta had a good start to their relationship (blackmail is never a good start to anything, honestly), but at the same time, if you decide to commit to being in a relationship with someone, there are some basic courtesies you owe the other person. For example, honoring requests that are not difficult shows you respect and care about the other person. Not being alone with someone your partner has told you makes them uneasy, even if you don't believe them, is not a difficult request. On top of that, Masaki was going to let the nurse have his way with him but stopped him because the room was dirty???? He had the ability to get out of the situation and did it because the room was dirty, not because he'd be betraying Sohta??? Sorry, but even I can't follow that trail of yaoi logic.