I'm glad that you were able to resolve the situation.
I was going to bring up a few concerns...
1-You mention that the discussion got heated. I've no clue whether that implied that you were insulting or disrepectful when you called, or whether the player simply didn't like the fact that you called him regarding cancelling the session without warning.
2-The player *did* cancel the session, and evidently didn't tell you about it. If it's a one-time thing, then maybe it was a pure accident. This can happen regardless of whether or not kids are involved. However, you also mentioned that it's not the first time this has happened. Consequently, it sounds a bit more like a pattern. And you mention that there are times you've driven an hour to the game, to have them cancel. To me, that's kind of disrespectful. In the absence of your note regarding this being your nephew, I'd have advocated being careful with this player, because of the possibility of the lack of respect. However, since he's related, hopefully it's something you can talk to him about. Regardless of whether or not he has children, common courtesy dictates that he commit to plans, and if he can't commit, he tell you. If his ability to meet those plans changes (due to kid or wife stuff), then he should let you know. You have taken time out of your schedule to commit to doing a mutual activity with him. You were there when you said you would be. I would hope that he can reciprocate for you.
Overall, sometimes real life intervenes.....gaming is only one type of passtime....but just because it's "gaming" doesn't mean that it should be treated any differently than making plans to meet another couple at the movies to catch this week's blockbuster, or going out to dinner, or agreeing to go skiing or whatever. You're committing your time to an activity, and making plans accordingly. You have the right to ask that people respect your time as well.
And if a parent is outright cancelling plans on friends, without telling them, what is that teaching the kids? It's modeling behaviour that we used to consider rude.
I have a cousin who recently had a baby. She lives in the U.S., and comes back to visit her family every few weeks. In three or four subsequent instances lately, she's called me regarding wanting to get together, have us meet the baby, wanting to see our new house, etc. etc. So she asks if she can come by on a specific night. On each of these instances, we've said "yes", and put aside other plans, and gotten dressed up, etc. to host our guests.....and sat there, waiting, hour after hour for my cousin, who just never shows up. Says she's going to.....but when we call, her family says she's "out", or "on her way", but never arrives. And we've just wasted our evening....because we could have been doing painting, or yardwork, etc. This has happened three times in a row now, and she hasn't even had the courtesy to call and say "hey, sorry, something's come up, and my daughter is crying, and I can't come out" *or* "hey, sorry I didn't come by like I said I would, X happened with my daughter, and I couldn't come, really sorry for that". Regardless of whether or not it's due to a child, it's disrespectful. She's not valuing our time.
You don't have to insult a person when you call them on this kind of behaviour....but I think people *should* be called on this kind of behaviour, as it's just rude, and if people keep doing it, the behaviour will continue. And if you have enough respect for yourself, you shouldn't be allowing someone to treat you like that....
I'm not meaning this to be insulting. Cancelling plans, or not showing up etc. is a real sore point for me. Once or twice is one thing....when it starts happening consistently, I start to feel like a doormat, or like I'm the "second choice plan" for the night, which is not a good feeling.
Now that I've finished that tirade, hopefully you've resolved things not only by apologizing for being rude to your player, but also by having *him* recognize that cancelling at the last minute without warning is itself rude.....*if he's doing this on a regular basis*. If it's something that's only happened once in a blue moon, then it's not worth sweating over.
Banshee