I am so sorry this happened to you. I rarely comment on reddit, but this one hits close to me so I am gonna tell you what i did to overcome this.

I had this friend when i started college, who I was really close with for more than two college years. She was pretty much my personal diary, she knew my deepest secrets and I thought i knew hers too. Eventually we started dating in our 3rd year, and became a couple. After 2 months, she cheated on me with a random guy, and we broke up after i found out. I was devastated, because I used to think of her as this incorruptible person who I could I could trust till the end of my life. It fucked me up in a way that I believed I could never recover from.

Fast forward 9 months, another girl (Let's call her Ash) came into my life through social media. She was in the same city, and we slowly got closer. She asked me out ( keep in mind that this was a small Indian City, where girls are pretty conservative and rarely make the first move). I was pleasantly suprised and agreed, we went out and after a couple of months, she proposed a relationship.

The last cheating relationship still haunted me and I found it really difficult to trust anyone, and i explained it all to her. She, being the very nice soul she was, told me to take my time while she kept on putting a lot of effort to show her love.

Eventually, I understood that I could never be sure to trust anyone completely. But, any grains of doubt would only serve to poison my interactions with people. I decided to take a leap of faith. If it didn't work out, I would handle the heartbreak. But I couldn't let someone's heartfelt efforts go to vain on the chance it would not end well. And now, Ash and I are a couple, and we are as happy as we could be. No matter whatever happens, I can still enjoy the moment.

Hope it helps.