My Little Secret Obsession Escalates

I'm a professor at a university, and I've always been this serious woman who doesn't take much to heart. But ever since my late 30s, I began playing with the idea of being treated as a little girl by someone who is dominant in every way, even though I am now in my early 40s. It started innocently enough, just exploring some age-play roleplay with a friend through text messages and emails. We would play make-believe scenarios where he was my guardian or older brother figure. As time went on, it became more intense. He began sending me pictures of himself dressed up in casual clothing like a fatherly protector might wear. The idea of submitting to someone who was playing the role of an older authority figure really turned me on. We'd send each other playful notes and messages with childish demands and whimsical requests. One day, things went further than expected. I found myself in my apartment at midnight sending a plea for him to visit me immediately, to protect me from some made-up danger that suddenly loomed large in my mind. He arrived, wearing jeans and an old flannel shirt, looking every inch the concerned big brother. As he entered, his presence filled the room with a sense of safety and warmth I couldn't resist. We ended up sitting on the floor together, me huddled close to him for comfort, but the closeness turned into something more intimate very quickly. Our roleplay had been playful up until then, but this night felt different. I leaned against his chest, feeling every muscle under his shirt as he stroked my hair and told me everything would be okay. It was a mix of protective tenderness and growing physical attraction that left me breathless with desire. We kissed passionately, it was like the lines between reality and fantasy blurred, and I wanted more than just roleplay. The night ended in bed, us both exploring each other's bodies under this new dynamic. The next morning, we talked about how far things had gone but agreed that what happened felt natural given where our relationship stood. Now I'm unsure if my feelings are shifting beyond the play and into something more serious, or if they're just part of my fantasies. What do you think? Am I crossing a line?