She didn't even *want* to go get a drink with Robin, Robin wanted to get a drink with Leslie.
Leslie realized how much she hates Robin's ideals means she couldn't bone her, even though the stated purpose was to bone her to fuck up her political bid.
After she totally gave up and brushed Robin off, trying to get her away from her since she can't resist her small congressional hands and hispanic charms. Then Robin got worried that Leslie hated her all of a sudden after they were getting along well, and offered to take Leslie to a bar to talk about things. Over drinks, Leslie revealed her lesbian backstory, Robin offered some pragmatic advice instead of commiserating or admitting her policies are hurtful.
Then Leslie accused Robin of being bi, since she clearly can't resist her sweet tits and educational bod. Robin protested and Leslie got up to leave saying she shouldn't even be here because she could do something wrong (read: ravish Robin, which is equal parts presumptuous and hot imo). Robin asked what she meant by wrong, Leslie touched her hands and referenced Steven Universe (implication: "Steven Universe and chill"), both of which got Robin wet as fuck. Then someone snapped an "incriminating photograph" of them with their faces close. Then Leslie left after stealing Robin's glasses that she uses to look smarter, because never pretend to be anything but who you are, even if that's a huge idiot.
Robin followed Leslie home, told her landlord something so she could get in her home, and then went to sleep in Leslie's bed. Now she's pissed because someone took a photo, and *now* realizes Leslie was all sexy looking to try and seduce her, which wouldn't work because she's totally not bi at all despite how thirsty she is for that Leslie love.