Ex discarded me and got back with her ex less than 3 months later.

I'm not really sure what I'm looking for by posting this, but man it hurts...

It's been 3 months since she left. We dated for 1 year and 1 month and I genuinely saw the rest of my life with her. You spend nearly every single day with another person from the first date onward and you really start to think they might just feel the same. Someone tells you they love you, want to marry you, and can't wait to have your last name and you start to feel some confidence in the strength of your relationship. You realize real quick just how much weight words hold when that same person calls you 20 minutes before a date to tell you they love you, but are no longer in love with you. You realize just how strong your bond is when they suddenly decide you're completely incompatible without ever discussing their issues with you. You realize "love" is just something people throw around like nothing when you're blocked and no contact a week later.

She was my first relationship and maybe it was that naivety, but she had me in the palm of her hand. I wasn't totally blind either. I knew we had issues, I knew what made her stressed, I saw her red flags, and I knew where I was weak, but I was ready and willing to work on anything if she wanted to sit down and discuss it. I tried SO hard to be the best boyfriend I could be and I would have continued to do so.

It's been 3 months and the words "I need to figure out my priorities" still echo in my mind. From the little info I've been able to gather, nothing about her life has changed outside of replacing me with an ex from 2019, and I've never felt so bitter. This guy she brushed off as "just a friend" suddenly popping up makes my blood boil. It feels like I was just a stand in for this guy. Someone she could use to fill the void until the circumstances were right for him to come back. I find myself spiraling, asking if they were talking while we were together, wondering if she ever loved me or if I was only a free meal and trips. I feel manipulated, and I can guarantee she's probably using the "nobody's ever treated me the way you do" routine on him as well.

I'm just bitter man... I find myself praying someone does the exact same thing to her. How are people even capable of doing things like this? Is it just more experience? Is it a difference between men and women? I could never.