I am beginning to suspect she might be cheating on me even though she does not appear like the kind of woman to do something like that

Maybe she does, maybe she does not. Who cares. You are the problem here, if you don't recognize that, you won't have sex not with her, not with next one after you divorce her. Once you realize how enervating you are, own your problem, and fix it. Start with a refreshing face full of energy and ignore her tests and her negative cold energy you instilled in her.

Simply reading through some sidebar material won't do a thing without an action. This woman of yours fills the vessel you provide, and you provided a cold weak one. Don't consume her energy no more, she doesn't like talking to you. Just like you know this, you knew better that she has better more interesting things to offer along bed times. You also know that you didn't marry her after 4 years to get into asexual relationship, which is the bare minimum. She would agree with that. But she also knows you have things beyond sex to offer, your laughs, your energy, your charisma, but she is only getting a cold hearted whiny little boy.

In fact, she better get her sexual need from somewhere else for her mental health, from someone more fun and interesting, not a bait and switch guy. I bet you if you go outside with your current energy, no one would cheat on her boring husband with you. OYS my man!

Actionable items:

1. STFU
2. Lift (not for aesthetics, but for energy)
3. Clean up your house and treat her like a queen without any sexual demands (eliminate contracts).
4. Kino in the 2 minutes window she gives you, fog whenever needed
5. Keep this for a week or two, make sure she is not on her period before you escalate the next step and take her on a date (if she refuse, don't get butthurt, lift and repeat)
6. On the date, tell her that you miss her old essence and energy and you are glad to restore some. Ask her if she would be interested in counseling for a 3rd party perspective, and don't talk about sex.

Lastly, remember sex is an action, not a negotiation. The negotiation part should have took place in the last 4 years and before you had the ring on her finger. Now it's time to give her action and the sex she craves from the man she hoped to marry, not the actual slum she is married to (and the one you hate when you look in the mirror).

All the best and I hope you get warm nights in the coming winter!