God I know that title sounds so generic but I'm searching for a B&W manga, pretty sure it was a one shot. Salient plot points:

Dark haired, plain/unattractive/very antisocial Main Character with glasses is asked by his lone friend (female) to pretend to be her boyfriend so that this light-haired, smirky playboy will leave her alone.

Later, the playboy takes the MC to a diner and asks about the relationship with the girl, eventually calling out the lie - but he doesn't seem at all bothered, instead he's interested by the MC.

Other scenes that I think happen (fuzzy recollection):

Playboy makes MC come out to a group date thing at his house. Initially a woman is pretty aggressively trying to get a resistant MC to sleep with her, but playboy steps in to stop it (and then gets the MC to hook up with him instead).

Also, a side character - cute, flirty gay guy comes in wanting to be with the playboy, is jealous and petty, but he finds a boyfriend as is eventually (sort of) a friend to the MC and the playboy.

Any help is appreciated, I wish I'd written the name of this manga down.

Pretty sure it's Hetakuso Love Step

YES. THAT IS IT. Thank you SO MUCH. So many bookmarked recommendation videos but I couldn't find the source for this one.