it’s less of technical terms and more of the cultural context applied to the term “ex.” “ex” is always interpreted as a partner who no longer is your partner due to choice (whether that be mutual or not), and ive personally never seen it used in context of a dead partner. ive met tons of people who just call them a dead bf/gf, since “ex” just felt untrue/disrespectful to the nature of their relationship.

The only chemistry mc had with ml is literally just sex
Emotionally he is still so in love with his ex and he knows that the author knows that cus outside of sex they don't have a single emotional connection other than mc feeling like he need to protect ml as his bodyguard and bc he failed to protect his ex before.