Well I haven't physically cheated yet, but mentally for sure. My wife actually has pretty good looks. She stays in pretty decent shape and is actually trying to get get into even better shape. My wife patterned our sex lives to where it was a weekend thing only (her days off from work) and at certain times (late afternoon). A porn/fantasy outlet for me let this slide for years. She stopped with the blowjobs, only wanted to be on top 90% of the time, etc.. The porn just allowed me an outlet to where I didn't seek an affair/cheating.
A few years ago I just had a breakdown and told her the issues. I saw what chronic porn use was doing to me. It destroyed my youth and I was just done. Things did get somewhat better, but she still has oddities when it comes to sex and it is very hard not to want to seek out someone who is more sexual, OK with sex being dirty, etc..
If she was more normal, I doubt I'd be tempted. Most of this is my fault for using porn as an outlet. I was desperate for a first LTR and she was it and instead of just dumping her after a year or two and seriously dating around, I stayed and we ended up married.
My past definitely plays a part in this. It was only very recently that I stopped the porn use and masturbation. I started to have serious regret in choices I made in life and what I missed out on. I wanted to be over it. I now believe that chronic masturbation may cause certain men not to be as driven to seek out relationships with women. With the co-worker, she is so open about sex, and I know lots of women actually can be that way. I was always scared to be very frank about sex and human sexuality. As such, I missed out on so much.
Hopefully things will continue to change and get better with our sex life. She doesn't understand how high of a libido I have and how much I repressed that using porn. She actually might be very open to change, but it is very stressful for her to deal with any change due to her mental condition. I still don't know if I'd cheat, but if I did it would mostly be an offer of a quick one and done. I definitely don't see myself having a girlfriend where we go out to eat, get hotel rooms and travel, etc.. I guess maybe since I only have had two intercourse partners in my life (and a handful of others that didn't get to sex) that maybe I'm drawn to just wanting to experience sex with other women now that I see what I missed out on in the past.
If my wife changes, I doubt I'd cheat. She is drawn to being a recluse though, and she needs to start dating her husband again. Going out to eat once a week isn't dating, but she thinks it is. Since she didn't want to have kids so I'd have something to focus on, she needs to be an active partner with me (hiking, going to swimming holes, etc.).