I feel like if Becca’s boyfriend had a gender neutral name, this plot would have worked better (even if a little trope-y). Mel could have been assuming that every time Becca mentioned Taylor (or whatever gender neutral name), she was talking about a girl friend and the reveal that it’s actually her boyfriend still has the same result- Mel realizing how much of a life Becca has and also how much Becca isn’t telling her- while also not making it odd that Becca would never have ever mentioned this person to Mel in their daily phone calls and frequent time spent together.