The answer is no. You already know the answer is no. But since I have been asked this question by actual adults, here is exactly why sharing colored contacts is dangerous and what can happen even if you share with someone you trust completely.
It Is Not About Trust. It Is About Microbiology.
Your eye has a unique microbiome — a collection of bacteria that live on your eyelids, your lashes, and the surface of your eye. These bacteria are harmless to you because your immune system has adapted to them. They are not harmless to someone else. When you share a contact lens, you transfer your entire ocular microbiome directly onto someone else’s cornea.
The receiving eye has no immune adaptation to your bacteria. The lens sits directly on the cornea for hours, creating a sealed environment where the foreign bacteria can multiply. The result can range from mild conjunctivitis — pink eye, which clears up in a week with antibiotics — to a corneal ulcer, which can permanently scar your vision.
Makeup Sharing Is Not the Same Thing
People share mascara, eyeliner, and eyeshadow all the time without serious consequences. The difference is that makeup sits on your eyelashes and the skin around your eyes, not on your cornea. The cornea is far more vulnerable to infection than the eyelid margin. A contact lens that has been in someone else’s eye has been sitting directly on their cornea for hours. The bacterial load is orders of magnitude higher than a mascara wand.
“But We Are Dating” Is Not a Medical Argument
Intimate partners share oral bacteria through kissing. They do not share ocular bacteria. Your mouth and your eyes have different microbiomes. Being in a relationship with someone does not make you immune to their eye infections. If your partner develops a corneal infection from sharing lenses with you, the fact that you are dating does not reverse the scarring on their cornea.
What About Sharing Solution or a Case?
Contact lens solution is not shareable. The solution in your case after an overnight soak contains whatever bacteria were on your lenses when you put them in. Pouring that solution into someone else’s case transfers those bacteria. A contact lens case should only ever hold lenses from one person. Mark the case with your name if you live with other contact lens wearers.
Colored contacts are personal medical devices. They are not accessories to share. At $9.90 per pair for Berry Series or Earl Series lenses, the cost of a separate pair is trivial. The cost of a corneal infection is not. Buy your own pair.