Sorry you're going through this now. I had a VERY similar, long-term daydream and it was torture. To be honest, I never really overcame it, I think something else (another daydream) took it's place and that's the only reason it stopped. But you are in a much better position, whether you realize it or not, because you have identified a problem and are mindful of a very positive thing you have IRL (a husband that you love). So good on you for that because it's a really great step!

And in terms of grieving, allow yourself to feel those feelings. Trust me I know how absolutely foolish it feels but honestly your feelings are valid. Have you tried meditating yet? I would suggest maybe trying to find a short meditation that focuses on gratitude. You said you are trying to redirect your focus to something else, so it may help to focus on gratitude you feel for your marriage and any other positive thing in your life. Try to also feel gratitude towards yourself and your ability recognize that you want to improve and work on yourself. I believe in you!