"Actually, I don't love you anymore."
Actually *我不爱了你 would be wrong. Only the sentence-final 了 can with either 不, the one directly after the verb and before the object can't (the negation of that 了 is 没有+V).
And actually 爱 doesn't go with that kind of 了 either because it is a "stative verb" – a verb whose meaning is considered a fixed state rather than an action or process (知道 is another such verb). This conflicts with the function of post-verbal 了 which marks perfective aspect, i.e. an action or a process which is viewed in its entirety, from beginning to end, and fixed states have neither of those. So you can only say 去年我还爱你, but not *去年我还爱了你.