No, it doesn't seem to be a popular story. I've never heard of it in mainstream media or among common story collections.
I don't think it's a popular story. Popular stories usually have a wide distribution, are adapted into different forms like movies or TV shows, or are talked about frequently. Since this 'young killer msodoki a new girlfriend story' is not something that is commonly mentioned, it's safe to assume it's not popular.
It's very likely not a popular story. There are so many well - known stories out there, and this one with such an unusual name like 'young killer msodoki' is not something that has gained wide - spread attention. It might be a niche or personal creation that only a small group of people are aware of.