Latest chapter (ch.27) seems to imply that ML is the father. He asked for the little girl's age which was 9 years old, and ML got kicked out just after FL and ML had sex around 10 years ago. So yepp both the math and the manhwa rules all point to yes, the ML is the father.
Another clue is how Sherry enjoys drawing . Especially flowers. The ML was also an artist and gardener and he would often like to give flowers to the FL.
So, is the Ml the father? cliché manhua rules would say so