Wow, What a horrible situation.
From an outsider's perspective it doesn't really sound like you are in love with this Sam. But I dont know you, I dont know your personal definition of love. Perhaps you are. What you sound to me, is mighty attracted to her. Her looks, her sharp mind, specific things about her that dont make a whole person. To be honest matie, you sound intellectually turned on, or physically attracted, either or both. Is it actually HER that you love? You may not be in love with your wife. You may have made a mistake there. But this Sam is a second issue. I'm probably way over the line here, and sorry. But what you describe with this other woman doesnt sound like the everlasting (or not necessarily forever), deep rooted absolute all out love you should be feeling for a person you trot down the aisle with. I think we use the term marriage, as I am, as simply a measure of the amount of love felt. You may not last with this one, you may leave and go to Sam, but may not last with her either who knows. Lets assume though that you can use marriage as a scale or a measure, do you love either of these women enough to undertake the marriage deal? Consider them seperately, as they are seperate problems you face I think.
You said something about your heart and head earlier. Your heart goes completely off feelings. If what this with Sam is all about whats coming rom your heart, I dont know if I necessarily agree thats what you should seek. I know love is all fo the heart blah blah. But your head is not telling you there is any sensible reason that Sam is the right one. You heart is all excited because her mind excites you, her body is all too appealing, her attitude make you swoon.
I dunno dude.
But please also remember, the honeymoon ends. What will Sam be like once you lose that heart fluttering sensation everytime you touch or see her? All relationships calm down. Our hearts cannot cope with the constant adrenalin you feel with Sam currently. She is the forbidden fruit, that is why you are still feeling it. She is untouchable, unchartered territory, and very very appealing. But one day that will be gone. Who will you be left with? Are you IN LOVE with the aspects of Sam that dont make you weak-knee'd? Because darl, if you aren't, you will be left with an empty loveless relationship when your honeymoon is over. And it will hurt.