People love more than once in their lives - it’s possible. The Doctor especially. IDK what will happen in his future, but just like loving River didn’t diminish his love for Rose, and loving Rose didn’t diminish his love for Romana or his first wife; someone new would never diminish his love for River - the heart is limitless Anon, and you will learn that as you get older. And it’s not dumb - it’s just that we are still in the River phase right now, so we are really attached. Really attached. But in the future, wouldn’t you want him happy again? River would.
Bah. I am bored and wanting my muse to start working again. Feel free to send in Doctor/River prompts that will be turned into fics.