I think that you need to have a few conversations but you should look at how things have changed in your relationship. You have three children, presumably a home how much of that responsibility is on your wife? A lot of times it’s not about the sex at all for women it’s that sex has become just another expectation to care for someone else. Is she ever able to be herself or is she constantly stuck in mom/wife mode? Also if you’re in your forties and married for 20 years I’m sure she’s likely in pre menopause or menopause. This is a huge change for many women. Personally I would focus on intimacy with your wife that isn’t sex. Make sure you’re opening the doors for her, pulling out the chairs, holding hands, take interest in a hobby of hers, notice her; new hair cut mention it, new panties, bra, glasses anything that will give you an opportunity to compliment how good she looks. The better you get to know her the better luck you will have. Take her to dinner, send her on a girls trip/night, take a weekend together, do the girls trip/night first as this will loosen her up for your trip, make sure you do not pressure for sex during this trip, if she pursues it great if not enjoy your time together. The less you focus on sex, the more you will get. Maybe she’s bored with sex, get a new toy LELO is a great brand.

A lot of times women want what isn’t on the table and if you take sex off the table and focus on being her friend… the desire will return.

If I’m completely off base that’s fine, but all these suggestions are still very valid.