I think I am being unreasonable here but I can't help but feeling irritated so I was hoping for some perspective from the outside

BM has always been well off (her father was a self-made millionaire) and now that her father passed away, it sounds like her inheritance is in the millions. We've been paying child support ($500/mo or 325 pounds) faithfully and plan to continue doing it until SD is 18 which is a year and a month away (but who is counting

$500 is quite a bit of money for us...but you do what you've got to do right. So now BM bought that boat she invited us on...that's fine. But this weekend I noticed SD has a Nook -a Barnes & Noble electronic ereader that costs $260. I think it's a bit pricey for a 16-year old. I've been debating if I should buy one but I am concerned about spending this kind of money and here she is sitting in my den reading on Nook. Hard not to feel resentful. This is what our child support is going to??

And last winter she didn't have a winter coat because BM didn't bother to get her one so we did that when she was with us.

Am I getting myself all worked up over nothing?