You weren't anything more than a fling to Slade.
Someone with no ties to his criminal work, who he'd visit every once in a while and stay long enough to entice you into some bad decisions. It was a break from everything, and a rather satisfying one at that. You didn't complain, you didn't nag, and Slade enjoyed your company. Hell, he spent more time pretending to enjoy the wine you shared and simply talking, rather than jumping into your bed with you. He lent you his shoulder to cry on if needed, he cleaned up after your pesky hangovers, he took care of you when you were sick. So, maybe Slade was being slightly delusional when he convinced himself that you were more than a fling. He'd had flings all through his long life, and this was crossing that line quite simply.
But a night of drunken passion before he went away for a long few months had left him with consequences he struggled to handle. He'd returned to your home to find you missing - your apartment empty, wiped clean, and your number out of service. He'd even enlisted Wintergreen's help in tracking down your location, but he was unable to pinpoint where you'd run off without a word. Must have payed someone good, he figured. Not good enough - eleven months of your absence finally led him to a cosy little apartment, and a resentful vendetta burning in his chest.
That resentment froze when he saw it - the baby. A tiny little thing (his?), all bundled up and sleeping, with a peaceful, scrunched up expression on their face. Slade did all sorts of mental gymnastics that would have put Nightwing to shame. He leaned down, carefully scooping the small thing into his arms, jolting them awake. Their nose wrinkled, loud, distressed cries echoing through the home. Silent footsteps came his way, tilting his head upwards to see you shuffle inside the baby room. The weariness in your eyes widened into a stab of fear when you saw him, flinching widely. Slade raised a brow.
"Been busy, haven't you?" He murmured, low and dangerous. "With our baby."