I would still recommend talking to your tax advisor. Your...

I would still recommend talking to your tax advisor. Your circumstances may be different to mine and there may still be a way for you to achieve the outcome you're looking for such as:
- selling the shares to your partner for next to nothing in an off market transfer so you can crystallize the loss.

Or even better:
- gifting the shares to an ex-partner for next to nothing so you can crystallize the loss and inflict misery on your ex. Two birds, one stone.