Credence is in love with Graves, but for any reason (age gap, situation, maybe he's genuinely not interested at first) Graves doesn't feel that way for Credence. Newt though, is very attracted to the boy. Credence doesn't reciprocate his flirting because he wants Graves to be his first, so Newt doesn't push him and leaves it at that.
However, Credence realizes Graves might get jealous (or maybe someone adviced him to try that to make Graves react), and he ends up having sex with Newt in a place where Graves can walk in on them. Which is what happens. Credence notices him, but what happens next is up to you (does he freeze and simply watch them? does he try to claim Credence? is Newt aware Graves is there?).
Credence/Newt, Credence/Graves - possessive!Graves, public sex (?)
Credence is in love with Graves, but for any reason (age gap, situation, maybe he's genuinely not interested at first) Graves doesn't feel that way for Credence. Newt though, is very attracted to the boy. Credence doesn't reciprocate his flirting because he wants Graves to be his first, so Newt doesn't push him and leaves it at that.
However, Credence realizes Graves might get jealous (or maybe someone adviced him to try that to make Graves react), and he ends up having sex with Newt in a place where Graves can walk in on them. Which is what happens. Credence notices him, but what happens next is up to you (does he freeze and simply watch them? does he try to claim Credence? is Newt aware Graves is there?).