You must have got into this situation for a reason be it good or bad what you need to do now is work out if you really do want out of this situation and only you know the answer to that. As for how to stop thinking about him firstly if possible try not to see him even for a second now that could be impossible but the longer you go without seeing him the more your mind will stop thinking about him. Distraction keeping your mind on other things will also help. It will take a while but I am sure you will get there in the end.
That's OK, glad I could help
look deep into your husbands eyes, watch him when he is sleeping peacefully.
It depends upon how he treats you. You want out just by asking the question. So, take it from me, I've been there, get out now, while you are not heart broken.
See a therapist to sort out your emotions and figure out what you want to do. As for the fantasy of leaving your husband and marring the other guy, there is only a 3% chance he would marry you and only a 0.03% chance that the relationships would survive more than a year.
Think about what sort of person would sleep with some-one else's spouse. Shame your self out of it.
Ugggg. Maybe go to therapy. I'm thinking you'll need support to leave.