Jason Todd

Earth-One / Post-Crisis / New Earth
While adventuring together, Jason harbored unrequited feelings for Donna Troy. (Countdown)
 * 1)  Rena 
 * 2)  Talia Al Ghul  and Jason slept together around the time of his resurrection.

New 52
Jason has pined for Starfire, who does not requite his feelings.At one point, he even lied and stated that the two of them had been lovers.
 * 1)  Isabel Ardila 
 * 2)  Essence 
 * 3)  Artemis  - After some romantic tension, she kissed him just before she and Bizarro were sucked through a door that could lead to almost anywhere, and pushed him so he wouldn't be sucked in with them. (Red Hood and the Outlaws)

- He has also flirted with both Supergirl and Barbara Gordon (the latter in Batman Eternal) - he might have also slept with Rose Wilson (but Deathstroke and the characters related to him were completely reebooted several times during the new 52)