Slow-burn fantasy romance with powerful immortal hero?

Looking for fantasy romance books with this specific vibe:

• Cold, powerful immortal / demon lord / celestial general hero

• Gentle but secretly powerful heroine (hidden lineage or sealed power is a bonus)

• Fated mates or lovers across lifetimes

• Forbidden love with divine or magical politics involved

• Lots of angst, yearning, and emotional tension

• Slow burn with a big romantic payoff

I love reincarnation arcs, memory loss, sacrifice-for-love moments, “touch her and die” energy, and morally gray heroes who only soften for her.

Any recommendations that fit this?