I have the pleasure of washing both my own kit and that of my boyfriend.

Sorry, but it sounds like your kit isn't getting cleaned properly and quickly enough - but whatever you do, don't say that to your wife!!

The smell may be old sweat coming in to contact with new sweat. Make sure you're washing your kit as soon as possible on a hotter wash than other clothes. 40 degrees is too low. It should never end up in a laundry basket, that's just gross.

If you're not able to wash straight away, such as after commuting to work in a morning, then at least rinse them out in the shower and wring them out before putting them in a bag.

Of course, this only works if you have multiple kits, so it depends how often you're riding.