Summoning the Sea's Mermaid Princess [Crossover]

I'm a mermaid, and I hooked up with a five-meter-tall hunk. Now I'm planning to cheat on him. But how can I cheat when I've never even been in a relationship? Admitting that I hooked up with a man is already making me lose it, and holy crap, he's five meters tall! How is that even possible? Maybe instead of cheating, I should get my sleepwalking under control. I'm so stressed I'm going bald.