Weirdly, I have two stories for this.

My first long-term girlfriend was someone I was with for nearly 2 years. She's a wonderful person and I loved her, but we were young. I knew, from the earliest points in our relationship, that she was someone that I could marry. I was scared of that. How could I, at 20, know that I wanted to be with someone for the rest of my life? I broke up with her, and we both went off and did different things, fell into our own depressive episodes, came out the other end different but the same. We've reconnected recently and she's still just as wonderful as I remember her being and I love her just as much. I have a lot of regret for how I acted, but I felt like we both needed to grow as adults before either of us was ready to have the kind of responsibility that we wanted out of the relationship.

After we broke up, I stayed single for a while, figured out what kind of person I definitely didn't want to be, and tried dating again. Met a girl who I was with for 3 years and it felt really good. We moved in together, I took care of her family like they were my own; we made sure that we were both happy. Or so I had thought. I had been struggling massively with depression and she was definitely one of the brightest parts of my life for the entirety of our relationship. When she started hanging out with some guy, I figured that I could trust her because she really meant the world to me. I left town for a weekend, and when I had returned she had moved out and wouldn't talk to me. I was frantic trying to figure out what was going on, clinging on to a hope that this wasn't real. I learned, from a close mutual friend, that she had been seeing someone behind my back, lied to my face about it, and left because I was too depressed to be around. Turns out she had been saying horrible things about me to other people while acting like everything was great when she was with me. It's really broken me down and has put me in a horrible state of mind. It has also made me question the validity of all of my relationships, as I really don't know at this point if someone is truly in love with me or if they are just pitying me.