To Ride or Drive...
I will sell my bike only to buy another, otherwise you'll have to pry it from my cold, dead hands. :D
But seriously, there are no certainties in life. I'd never sell my bike just "because its dangerous". Lots of things are dangerous, and you don't get any say in a very large number of them. You can just as easily have a heart attack, get cancer, whatever. If you enjoy riding, then enjoy it. Nobody gets out of life alive, and very few get to leave happily on their own terms. Get a nice life insurance policy if you're worried about your family.
Now, if your bike is just going to sit in the garage because you simply don't have the time, that's a different story. Especially if you can use the money to build your Valiant. That's a sound financial decision. Obviously, keeping the bike and building the Valiant would be great too, but not everyone can afford to do that. And if you and your new family can all enjoy the Valiant, even better.
Don't worry about all the marriage talk. Well over 50% of all marriages end in divorce, so as a "commitment" its pretty much useless. If your partner doesn't trust you to stay around you've got bigger problems, and putting a ring on her finger is not the solution.
My significant other (girlfriend, partner, whatever you want to call her) and I have been in a committed relationship for over 10 years. Longer, I might add, than several of my friends marriages lasted. I'm happy, she's happy, why mess with a good thing. Do what works for you.