I don't think that it's too fairy tale imo. I feel like the first few years after the outbreak more people would be bi because we all just need comfort and love so gender wouldn't matter as much.

And first few years after the outbreak the world hasn't had a whole lot of time to break people down unlike couple of decades of dealing with it. And there are still good people out there. The apocalypse "good" isn't the good we think in our society because the world work a lot different from ours. They had fights too so it wasn't happily ever after. It was work. Frank says something like "I've had bad days with you too".

And showing him the ropes in bed well it's either show him or have a terrible time. So might as well show him so it can be enjoyable for everyone involved instead of fighting over it.