Yes it's a sad situation, but IME very common! Some people don't need passion as such and prefer stable non-fiery partners whom they like as a friend. I relate to you though, OP, been in similar marriage myself - though maybe not as good as we weren't really close friends (lots of misunderstandings), though we did like each other generally and shared sense of humour, and we did have a passionate spark in the beginning. It's disappeared after a year or two, because that X element of true love was missing, I think for both of us. He was also decent and well-to-do but very immature (so was I).
We divorced (no kids) because I was feeling very trapped - and worse, my head kept being turned by others, he just retreated into himself and his work. If you can avoid getting to the stage when you feel suffocated, then do it! Either go to a VERY good cousellor, or think of parting your ways. You are very young at 31, and you have a dc, and could meet a true love, though of course there is a risk. But if you don't do or change something you are in danger of falling into depression OR having an affair, and he's not immune either(!) if he feels like you don't really love each other.
As someone said, yes it could be a whole lot worse. I still haven't met the right man in the years that have passed, but even though it's been quite hard, I don't regret that I left, it got to the stage emotionally that I didn't have any choice, to preserve sanity I needed to be free! It's much better to be single or date unsuccessfully then feel that you have to pretend to be happy and to have to spend all you free time with the partner you like but don't love - it's best to stay friends with him instead. I'm an emotional person, and you sound like one too, some people are practical/sensible (your Mum?) so yes, it could work for some but never for others. sorry for rambling!