This really isn't that complex except it doesn't fit the standard dominant heteronormative story for dating. Those stories where your eyes met across the bar and you fall in love with your new partner instantly. You either then stay together forever in the "success" story or fall apart in a dramatic fashion and never see each other again for a "failure" story. This isn't common and real life is more messy for these "failures". Just note that most people leave out the mess when telling their romantic "success" stories. I dated / hooked up with lots of my wives friends before we are started dating and so did she.
You had your best friend / roommate were / are a "failure" in this model but a success in real life. You made a real friendship out of failed dates and romantic relationship. That's a success.
Just be upfront and honest with everyone. Make sure your roommate / best friend agrees that you don't have a romantic future but rather what you currently have. Tell your future dates a simplified story about your roommate upfront and everyone will be cool. You got this
I agreed with you until the last paragraph.