If you take nothing else from the segments of combat and physical pain that Frederick has undertaken, please consider the sheer pain tolerance he has built up at this point. Including not just blades or bludgeoning weaponry, but more exotic things including getting shot in places and directly being struck by Ice Magic repeatedly, for many years. Like, I get that some call it 'torture porn', but I'd much rather do those segments than have to explain repeatedly about Frederick's tolerance for pain from such a myriad number of sources, his familiarity with so many weapons, etc. They are a rather important show, don't tell, as to how he has steadily improved and maintained his martial score over the years.
Less amusing about haha sex things, however, is how deeply troubling it is on a fundamental level that that one of those most vital of things - tactile sensation - so immediately brings swift pain to Frederick's body. Being in Natasha's presence literally, factually, brings harm to her family members. The younger children, and grandchildren, cannot stand to hug her. The press of her lips upon their cheeks or on top of their heads do not bring giggling shrieks of childish denial at open displays of perfection. She cannot hold their hands without them shrinking away or wearing double mittens.
Where once, in bed, she and her husband could lay beneath the covers with nothing on, Frederick must literally wear winter clothing to survive the night.
And when she is happy? It gets worse.
When she is sad? It gets worse.
When she is in love? The throes of passion? The cold grows colder, radiates further.
Can you imagine how horrifying a life that could be? She can never make it go away. She can never make it 'less' beyond the 'barely alive temperature' as described before, a level reached only when she's fully relaxed or outright unconscious.
Her love hurts.
For all of that, however, Frederick has not, nor will he ever, consider setting her aside. He will bundle himself, he will put on those layers, and he will ensure his warmth is enough to continue embracing her, kissing her, and so on. Even if it does literally cause him pain. Every. Single. Time. Even if he were to lay against her for a full night bringing the danger of frostbite, of blackened and dead flesh.
And it is that acceptance of the pain she causes him which so bitterly mirrors the pain he has caused in her by leaving to battle and undertaking potentially fatal acts.
But they accept that pain, and move forward.
Because he has all her love, forever.
And she has all his love, forever.
Forever.