This is somehow weird and uncomfortable in addition to making no sense.
I can't add genre tags because I have no idea what was supposed to have just happened. Translation issue? Or does the source assume some prior context?
I mean, personally, that was one of the (many) possible explanations that went through my head as to what the hell was supposed to be going on. Which no one knows for sure, I think, thanks in part to the, er, quality of translation.
I don't think it's correct (and I think whoever has since removed the tag was right), but for me this interpretation would have hinged on a few things:
1. The best friend's occasional faces of horror/anxiety/sorrow, plausibly disproportionate to the situation, supporting an idea that something unsaid is going on.
2. The general focus on their intimacy and closeness, whilst "that guy," off-screen, who's the ostensible love-interest, we know almost nothing about other than that he's objectively kind of scummy.
3. The utterly garbled message at the end plausibly being maybe something bittersweet about the two girls, even if we're not quite sure what (but the first line, "if my feelings are conveyed," would in that theoretical context be between the girls, rather than towards the guy, so perhaps something like: "Even if you understood my lesbian feelings, I know you would pretend not to know," for a classic girls-runs-off-with-guy yuri-angst premise).
4. Finally and purely contextually: For those unfamiliar, how common "I'm doing my best to pretend to be in love with the other gender because I can't admit I love my best friend" is as a plot setup in yuri/yaoi, combined with the fact that none of us have any context for the intended audience, nor an English plot summary, to give us hints as to what we're reading and how to interpret it; important especially with something of this short length where we're expected to fill in some blanks.
Just providing some context to your literal question, why the tag got added, as to how someone could read this like that. Again, not, I think, what's actually going on here.
Since absolutely no one knows what's actually going on (unless they can find the raws and read them maybe, I guess), the current paucity of tags seems about correct. Though I'm tempted to remove "slice-of-life" since it isn't really. Just call it a oneshot and be done XD