Today at work something just hit me in the gut; I couldn't stop thinking about her making love to this guy...
I know exactly what you're going through. Still happens to me, although less frequently. Would it help if I told you it'll get better with time?
Do what you can to cope. Channel your energy, if you can. Make yourself go outside and exercise. Exhaust your body.
Meditate, if you can. Bring yourself to see her as a stranger that she once was. Or think about who she has become, all that she's doing now to hurt and disrespect you.
Might help....
Me: 50, MLC/WW 45 Young kids Nov 2015: BD1 Apr 2016: BD2 Jan 2017: W filed Feb 2017: D final