Few people are waiting for game completion but rather intercourse and depravity which will occur far sooner than game completion...although admittedly far sooner is still probably ~1-3 years away
If we're talking about intercourse on the filthy wife route, the first possible extramarital sex is scheduled to be happening (unlikely) on PD16, which is a lesbian scene, and we don't even know if Sophia is involved here at all, as the only information we got is that there's supposed to be "important characters" involved. If we were to assume that this actually includes Sophia, and it's most certainly not happening at the beginning of PD16, that means it's gonna take roughly 4-5 years with the current development pace to get there.
If you're talking about the first possible hetero cheating scene involving Sophia, then that's gonna be PD19 according to some comments from different users on here, which is 6 entire PD's away. Again, with the current development pace, you could consider yourself lucky if the game reaches this point in about ~9 years from now. Possibly 8.5 years if this scene is gonna happen right after Sophia wakes up on PD19, which I highly doubt is going to be the case.
So, unless a miracle happens, your 1-3 year estimate is completely unrealistic. Stop lying to yourself.