lime

From a female perspective: STOP STOP STOP "helping" with chores!!! It can do several harmful things:
1. Make her think you're only doing it for the sex, like you said.

2. Make her feel inadequate--like she doesn't have the ability to hold up her end of the bargain. This will lead her to try and find other ways to feel superior to you to make up for her feelings of inferiority in this department...Guess what she'll do? Wield more power in the sex department.

3. Make her lose respect for you, like you're trying too hard to please her. When you "help" you're following her orders which means you're not being the strong, confident man she wants you to be.

4. Make her mad because you will have taken away her one "excuse" for feeling tired all the time. It's like you outsmarted her, and this will just irritate her.

It can do one helpful thing:
1. Make your house look a little cleaner.

You have kids. Their sole purpose in life should be to do all the chores. Haha just kidding, but they do need to learn how to help! This will actually teach them a lot of valuable skills in life so get your wife on board and get them to start helping more. It will alleviate stress without making her resentful of you.

MORE CHORE SUGGESTIONS:

1. Make a plan together of who does what. "Helping" out here and there sporadically is bad because it makes her uncertain of when you'll help or not. Consequently she'll start demanding it more. People like routine, it's comforting and reduces stress.

2. Own your ****. If you agree to do a chore, do it well and don't complain. Complaining makes you look weak. If she complains, don't just step in and help her--it will encourage her whining. Instead, sit down and discuss the possibility of reorganizing the responsibilities. Don't ask her advice of how she wants the trashbag to be tied, the forks to be angled in the drawer, etc. This is just petty B.S. and her way to control everything and feel smug and superior...Do it your way and if she whines, keep doing it your way, respectfully of course. Don't let her boss you around unless she has a calm, logical reason (ie: youngest child has been stabbing himself with the forks by accident).

3. Every time she whines about chores or is stressed with that stuff, listen politely but don't indulge her. Chores are not that hard. She's likely channeling stress from other areas and blaming it on chores and you. Don't let her do this.

I get that chores aren't your problem, but many women like to blame everything on chores. You want to eliminate the problem and her ability to use chores as an excuse--but you want to do it with her on board...If you sneakily try and eliminate all potential excuses, she'll just get mad at you (see #4 above). You want to do it together as a team so that she gains respect for you and so that both of you are less stressed with stupid unnecessary stresses like chores.

OTHER ADVICE:

Start working out more, at least 3-4 times per week. It's healthy for you, it will help you relieve stress, and it will make you more attractive. It will also give you something to do that you're completely autonomous over; you want to appear strong and independent, not clingy and needy. Your wife might appreciate the extra alone time she has to herself and she might even miss you when you're at the gym. You will set a good example for your kids to live a healthy lifestyle. This can do nothing but help you, I promise!

Along those lines, develop some more hobbies that you do on your own. Get in touch with yourself as an individual, start being more independent. It increases your attractiveness and lessens the severity of your marital problems.

This was really really long haha, but I hope it helped in at least some way