step-Mom realizes you've never brought a girl over, taken one on a date, or even talked about one. Because of that, she wondered if you were into boys. If so, that was okay - in fact, she'd help you become more open about who you were and what you liked.
She'd talk to you about cock and show you how to pleasure one using a cock dildo. Next, she'd have you try sucking it yourself. She noticed this aroused you, so she'd have you stroke your cock and pinch your nipples. She wanted you to stick your fingers inside your tight butthole.
She wanted you to think of a guy you might like while you were jerking off. As she used the dildo to fuck your asshole, she wanted you to think of a man fucking your tight booty and tickling your prostate with his cock. He'd fill your butt with his cum - you were a little cum dumpster. She wanted to see you cum. What a good gay boy you've been!