1. Yes it is polyamory. I had a (mostly) emotional affair to a man for 4-5 years. Is what made me realize this is "my thing". Us not once being naked together did not make an ounce of a difference, it is just that adding sex adds more pleasure! We still went through the whole cycle of falling in love/New relationship energy, a more stable phase of love turning into Long relationship energy, a more problematic phase of re-orientation towards the future, and an emotional break-up and now trying to get along as loose friends.
It don't totally see the accusations about "secrecry". He told his wife the moment he realized it was something more than friendship going on, what more can anyone do? Especially when they do not expect polyamory. One has to work from one's standing point, and in that respect you have done no wrong.
2. The kid anology only works when you have felt poly (plus it does not sit well in most people's stomacks to compare sexual love with the love for a child). The best anology is to say it is simply about love, but a generous love. "Love is like a magic penny..." And there are real limitations, like time, but it is not neccesarily so that spening less time makes one feel less loved, because it is also about what happens during that time, and also time could be taken from other activities to make the relationships priority.
3. Your situations is a BIT similar to me and my "ex", although I knew his girlfriend too and my ex's girlfriend watched us falling in love so there was no specific time where she needed to be informed. Similarily, I almost broke off their relationship (and I did break up their engagement. They even took time during their engagement party to discuss his feelings for me!). Looking back, I feel rather naive for waiting so long to actively discuss the issue, but is was also a matter of my husband only feeling half up to it, and I did not have an active polycommunity like I do today. Anyway, at the end of the day I felt that the two of them were not up to the task of intermingling our families (well, on a bad day I would describe it more in terms of she being a lyer and he a coward, but the end result is the same: them not being capable). I hope for you that you are luckier, and perhaps more clever, in putting your wants out there and making them into relality. If you are reader, I recomend "Opening up" (Tristan Toarmino). Best of luck