Hello dirst69juggalo. I think it's wonderful and big-hearted of you to want to continue being with this woman. It says that you love her. But I understand the "can't stop thinking about her and someone else". That part is your possessiveness and insecurity. Insecurity is obvious, and may be easier to deal with. Try to find the underlying thoughts/beliefs, because they usually are patently not true and once you bring them into the open you can LAUGH at them, but when they lie in the shadows, they can drive you.

Posessiveness may be more difficult to get over.
It is such a common malady, that often what passes for love is NOTHING BUT pure clingy posessiveness with not a shred of genuine love attached to it. We really, really do not give a hoot about the other person's happiness, feelings, personal development, satisfaction, pleasure, or desires, all we care is what they do for us. They must love us, and take care of us, and never ever look at anyone else, for we may feel threatened if they do. Because I love you, you are mine, my slave, I own you, I own your body, I own your sexuality; all your affection is MINE, MINE, MINE and no one else's. You've heard of men getting envious of their wife's love for the baby? That it. It is ugly. It is also very human. We are immature little boys and girls. Selfish. At least in part.

So how to deal with those imaginary flashbacks of yours? Don't try to suppress them. Whatever you push into the shadow gains power over you. Bring it into the light instead.

I would suggest to talk to her about it. Don't accuse her, but tell her how you feel. Tell her not as the one who is to blame for it, but your friend and companion for TEN years, one who can understand, one that may keep your heart safe when you open it up to her. Be gentle with yourself over it, be gentle when you speak, don't let it become a slugfest of accusations, instead make it lead you to a new level of intimacy. "Honey, here is my heart, I love you, I want to be with you, and I am having this horrible problem, that just screws me up". Let yourself be vulnerable with her. Make room for her compassion. If this sounds just too freaking weird for the two of you, perhaps you can have a help of a couples councelor to facilitate your hearts talking.

The other thing to try, maybe try as well, is to reconnect with her in some new way. As if you just met, and just started having a romance. In modern world we usually manage to get over the awareness that our new bf/gf is not "brand new" so to speak. So try that. Maybe try some new sexual ways. Like some Tantra practice, connecting your heart chakras and breathing together or some such. Talk it over with her. Maybe she's been reading stuff online "how to get your sex life to a higher level" kind of stuff and getting interested, maybe there is couples retreat of some sort that you two can afford.

I wish you the best of luck. Hope you and she manage to make your relationship grow stronger from this.