On the other hand, Jeffrey is fucking doing everything he can for Lottie and he fucking deserves the world for it. Take note that they've known each other for more than a hundred of years. Imagine how long he had stayed by her side and helped her in many ways. We even got a flashback that Lottie was telling Jeffrey about the curse and some important stuff in the past. They're really close and trust each other so much. Notwithstanding the fact that Jeffrey was the person Lottie run to for help after she supposedly "died" and needed a new identity.
Also, based on a rough translation of Chapter 51, when things were getting worse and Lottie was feeling helpless because she cannot do much and lacks power, Jeffrey came and saved her while saying: "Lottie, I always think it's a problem. You are not alone. Why do you always try to be alone? Everyone here (i.e., him and her disciples) is your magic and sword." BEST GUY AND VERY HUSBAND MATERIAL

If you will still ship Lottie with the Demon King after this, then you rather have an unstable violent man than a mature reliable one.