That's the problem then, old saves are not fully compatible for this version.
That can sometimes be a fair answer but in this case, the same save either has an error or not depending on an answer to a new question.
As you release the way you do, creating errors like this that require a new game every time is not wise.
It's simple to fix as well. The same way you set YGirlfriend = 1 in one situation, just make sure you also initialise YGirlfriend = 0 in the others (e.g label GirlfriendNo). Or even better in the previous dialogue before an answer is given so it applies more widely (e.g. if you tell him to leave you alone, i.e you should put it in label OutsideMorning)
And you should apply the same principle with every new parameter you introduce in new releases.