Looking for advice on how I should handle an upcoming situation with an ex. Been lurking TRP for a very long time, but I have never seen this covered.

I (30/M) was seeing this girl last year for a relatively short time. She was recently off a broken engagement and in a fling, but from the moment I met her I knew I wanted to be with her. I made the right moves and ended up dating when I was suddenly offered an opportunity to move to a city I've always wanted to a 10hr drive away. I really liked her, but I took the opportunity and moved. We agreed to keep dating LDR-style and see where it went. She came out to visit a few times, and I really thought there was a future. She started talking about moving out there with her best (f)riend in a few months, and I was thrilled. Really thought I had found someone special.

Then after a few months, she casually mentioned one evening that she was considering going out with this guy she had met on her volleyball team for an afternoon of boating/BBQing on his boat near the lake, just the two of them. Even now as I think back to it, I can still remember how awkward she sounded as she tried to throw that stupid little shit test at me, trying to have her cake and eat it too. I know this game though, I told her that I was feeling like we were past the fling stage and that I wanted a serious relationship. She said she wasn't ready and suggested we should just be friends.

I was pretty broken up, but I immediately put her on the No Contact list. She texted me once or twice during the No Contact period, both times I replied politely but dismissively that I was busy and would get back to her, never did. Deleted her from Facebook. I started working out and lifting hard, something I've never done before in my life. I went out to meet new people, I started eating right. Then, after a few months, I secured a new job making significantly more than I was before with a much better title. People started commenting on my improved physical appearance. My friends took note that I was doing really well. This past week, I put an offer in on a really sweet condo with a view, hot tub/pool and a real modern look. Heard through the grapevine she was dating someone else shortly after me (Gee - I wonder who!?), but other than that we've had zero contact.

All in, she dumped me in August and since then I've worked really hard to increase my SMV - originally to get her back, but now it's 100% for me. I feel great with my new awesome job, my new awesome condo, and my new improved body.

Anyway, her best friend still wanted to move after visiting last summer and it looks like she's going to move in to the extra room in my condo, so we're going to be living together. Strictly roommates, she's paying me market value rent. I'm looking forward to having a good looking and cool female roommate as social proof.

Question: My ex is coming up to help her best friend move in with me, and she'll like visit from out of town occasionally after that.

How should I act around her?

I'd prefer that I didn't have to see her at all. I still have feelings for her, I still miss her, but I 100% realize that she dumped me for someone else. I respect myself enough that I am not going to hook up with her or even remotely entertain any hope of getting back together with her.

But how should I act, what vibe should I give off? I know it's childish and petty, but honestly, she hurt the fuck out of me and I want her to regret her decision.

TL;DR - Ex dumped me for someone else. Immediate No Contact and I used the pain to lift, learn, earn and own more than ever. Now she's coming up to help her best friend move in with me. How can I make her regret her decision to dump me?