Alexis will be NTR-curable, but not before she does some nasty stuff first so it will be up to you do decide if she is worth it.
Maybe add a third option? If the player non stop cheats on her ( which we can guarantee, going by the statements from all the gentlemen here
), and you have a high scores ( kink, fitness, charm), then MC turns the tables on her and she goes desparate to "reclaim him".
Then you have the option of comitting to her or she ends up in relationship where she's being NTR-ed.
Going by backstory, MC/Mike was a sort of shy, unassertive guy before the game starts, it makes sense why he got burned with her/Samantha.
This seems to me more logical, and better option for a lot of players. ( plus most probably wouldn't give a damn about her, since you have way more, better LI's)