Me and my roommate were dating and we didn't noticed

For years I had this online friend, eventually we both got jobs we could do from home and we were tired of living in our cities so we decided to move in together as roommates in another city.

We were not dating (yet), he would go out and bring people over to be with, and so do I. We had no problem talking about our sexual life, fetishes and so on. One day he told me he really wanted to sleep with someone but was too lazy at the moment to go out so he just asked me "wanna fuck?", it was so casual, so natural, and I just said "sure". We kept doing that for some time, it was just when neither of us could get a date, then it became more regular.

Then one day, we were both watching a movie and he said: "so hey, are we dating?"

I paused the movie, "are we?" I asked, it was a genuine question.

"I guess? You feel like dating someone else?"

"Not really and you?"

"No. So I guess we are dating"

"Fuck."

"Right?"

"Wait for how long we've been dating?" I asked

After a long silence he said "I don't know. Wow."

"Me neither."

And that's it.