Honestly, this was me a few years ago. I'd had previous wobbles but worked through them and convinced myself that what we had was enough. We'd been together a long, long time and had a child, and there's no doubt that over the years, he'd stopped seeing or valuing me.
I asked myself a few questions
If you could change something about him, what would it be?
If you could change something about the relationship, what would it be?
How do you want to feel when you're with him?
Think about a holiday in a year's time with him - how do you feel?
Picture a really happy memory with him, how does that make you feel?
For me, I realised I was beyond wanting something to change, I'd mentally checked out and it wasn't fair to stay. While I kept painting him as a lovely guy, actually he wasn't a great husband and once I started to see things clearer, I couldn't not see them and I couldn't stay.
It was a hideous time, but I did leave - the bravest and most selfish thing I've ever done - and it took a LONG time for me to come to terms with it. We'd been together 17 years and being without him was a huge adjustment. I hadn't realised how different we now were and how we wanted very different things out of life.
We have co-parented our son who is now in his 20s and I'm fond of exDH. It was bloody hard initially, but we've gone on to have amazing lives apart - we've both been married to our partners for a long time. I went on to launch a business and have more children, and he's gone down a different path, and we are both so much happier.
Dig deep and ask yourself the big questions - you might be bored or feeling restless, or hormones are at play, or lots of other things. Or, it could have run its course, and you've just realised before he has. Either way, treat yourself kindly - you don't have to be a villain for wanting something different.