I somewhat agree with your first comment but I'm afraid I have to disagree with this one. The world is a huge place with billions of people, so how can you say loving someone enough to let them go only works in fiction when you've probably never even met a million? I personally have met someone who went through this exact circumstance and while yes, humans at the core are and will be selfish, but we're capable of genuine love too. We're capable of setting our loved ones free so they can be truly happy, we're capable of putting other people above ourselves (and this not just purely in a romantic setting). Heck, movies were inspired from that sentiment; poetry, music, even books! But media aside, for that to be possible in real life, you gotta put in the work to heal, to grow, to forgive and to accept.
This though? In Eclis' case? It's not love. It's obsession, the incredibly toxic and unhealthy kind. He only loves himself, loves what he can feel when he's with Penelope, loves the benefits of possessing her, but he doesn't love her, Penelope the person herself. Even the Prince, obsessed maniac that he is, is levels above Eclis because he truly looks out for Penelope. He walks the talk and seeks to be her equal through conversing with her, spending quality time with her, and just overall truly getting to know her.
My point is, humans are indeed selfish but love is real. And real love is more than just an emotion, it's a conscious choice. It's a lifestyle. You gotta believe in it if you wanna see it, and you can only believe it as you put the work in yourself.

Yeah, Until he locks you in the basement.