My (now ex) wife was against buying it because we had not bought a home for ourselves yet, and even trying to explain that we could buy it, live in one side, rent the other for the full cost of the mortgage and then some was not enough to convince her, so I let it slide as no amount of money was worth the never-ending argument that it would have caused.
That duplex is worth about $450k now, and if I had gone through with it it would have generated a conservative $200k in rent income in the meantime.
If I had known the relationship would have been over in less than 5 years from that point, I probably would have bought it anyway, but at the time my mentality was "happy wife, happy life", naively thinking that there was a way to make someone happy who refused to be happy.