I honestly don't think she banged the other dude. This manga, in comparison to others, has made liberal use of MC kissing spider chick so why wouldn't it show them banging or at the bare minimum a kiss but it instead she turned her head before anything happened. Also, there were like 3 pages of exposition where anything could've been placed behind it instead of them hugging in the moonlight.
She also ended up throwing him away, so I really don't think she cared that deeply. I just guess it's just up to interpretation.