It would be like fake dating, except only one person is aware of it. Obviously, they fall in love, and that proves that the person lying was in the right all along, but they're also wrong because they lied. The 70% conflict can be a gotcha reveal, or maybe the liar's lies catch up with him.

It ends well only because I write it.

If you take my advice, remember you cast me as a meddler and brought your own ruin upon yourself.