Depends a lot on context! I think in RL someone saying that to me would just not feel realistic? I can’t picture a partner needing to express undying love to me in this way. But like, a conversation about souls, after life, soul mates, not inherently strange.
In a romance story, I would not necessarily find it strange. I kind of expect ha heightened unreality of emotion in such stories, so it could easily be romantic written in the right way. It could be an intense expression of love. It could be a hint at a story with a supernatural edge and perhaps a lover willing to cross boundaries to stay together. Or as others have said, a super creepy “I’ll keep the body in the house and keep talking to it” kind of thing.