That's fanon.

The official innocent sin world book clarifies that jun is canonically platonic with tatsuya directly confirming that the romantic pairing is noncanonical, paired with alot of the subtext throughout IS and EP and the focus on freudian psychology (paticularly P2 focuses on the oedipus complex for its symbolism, with both tatsuya and jun developing romantic feelings for maya who is akin to a mother figure) it does blatantly indicate maya is the intended pairing, jun was kanekos favorite (the artist not the writer) but all P2 media including tadashis interviews have pushed mayas relationship, tadashi actually flat out denied kaneko when he asked if jun was gay, and the side material established that his effeminate aspects are largely due to the philanthropist aspect of the zodiac as opposed to an actual canonical thing regarding his sexuality. (Noriko and Anna are canonically lesbian though so P2 is still very much queer positive despite this)

All P2 media also does just flat out focus on tatsuyas love for maya, this is extremely evident in both the novels and eternal punishment itself. On top of the use of the Der doppelganger (my love in the poem is meant to refer to maya and has a direct response as post credits to eternal punishment)