in my saves where ian sleep with lena and with alison, yes she talks about jeremy about a threesome too. basically the premises is if ian does sleep around with other girls besides alison, alison will see ian as a sex friend and she will ask ian if he's fine with her sleeping around too. but in my main saves which ian only focus on alison, there's no trace of alison speaks about jeremy and she speaks about her relationship with ian earnestly.
since the first time this game has come out, i always play the alpha and the final version, and i've never encounter any problems at all. i think it's just because this game is so complex with the choices that a lot people might miss a lot of path.