stats on an item are not considered when equipping it

So I just unequipped an item that has +16 dex on it, and I can't equip it again because now I don't have enough dex without it to wear it lol

Working as intended.
Equip another item with sufficient dex or allocate a Dex node in the tree.

You can't equip items you can't equip, the bonus attributes aren't active until it's equipped. This is the attribute house of cards. If you can, find a Jade Amulet to toss on to permit you equipping your lost item again.

In addition, crafted dex enchants could help sidestep the issue, but often I find the big culprit is a high level gem that can be removed to fix the problem.

But I do suggest being careful with the house of cards, and being mindful about just how big of a fall happens if you get married to gear that is too outdated to survive.