Yes I know this is a depressing one but don't worry, I'm writing a positive one to come immediately after this
Connor - you had decided to end things because the stress of both of you working for the DPD had gotten in between the love you had for each other as well as neither of you being able to spend time with each other much. You both agreed to stay friends afterwards but how could you, while working in the same place and seeing each other every day? Being reminded of how much you needed each other.
Markus - he decided to end the relationship because with the upcoming android revolution, he knew he couldn't take the risk of you getting hurt and losing you. So he decided to let you carry on with a normal human life while he carried on with his chaotic android life. Until he realised how empty it was without you.
Kara - you both broke up due to a misunderstanding surrounding Alice. Kara thought you had neglected her when you really didn't and it wasn't your fault at all, but she didn't believe you. So you decided to break things off if she couldn't trust you.
Gavin - he always had a fear that he wasn't good enough for you and one day, he let that fear take over. You both had gotten into a pretty large argument about how you thought he didn't care enough for you and you ended the relationship out of anger. Instead of running after you and trying to convince you he loved you, Gavin let you break it off. Because he knew he wasn't good at giving you what you wanted.
North - eventually, the hate she had for humans seemed to dominate everything that happened in your relationship as she'd get mad every time you interacted with anyone who was human. Her own prejudice made her judge you, in turn and so she decided to dump you which led you to go in a downward spiral.
Luther - you both still loved each other but decided to carry on as friends as you both knew that a relationship between a human and an android would never work out in the long term.
RK900 - his own trust issues got in the way of your relationship as he grew more and more jealous. One day, he became under the impression you'd cheated on him and he decided to break it off without hearing what you had to say. Angry, you swore never to speak to him again. If he couldn't trust you, what was the point of trying to convince him otherwise?
Ralph - the authorities found out about the abandoned house you both lived in and they took Ralph away for questioning as to why he left his job. Before he left, he decided to end things so that you weren't left hanging or waiting for him for too long. He ended things so you could move on with your life.
Kamski - his return to CyberLife meant that he barely had any time to talk to anyone. Despite being the CEO - meaning he could take breaks whenever he wanted etc - he was swamped in work and felt too stressed to make time for you so he abruptly ended the relationship without giving you an explanation.
Simon - he was paranoid you'd leave him for someone else and to get rid of that constant paranoia, he decided to stop the relationship before it went any further. His fear of being hurt stopped you from proving him wrong.
Josh - he was under the impression that a relationship between an android and human could never ever work out and that was the explanation he gave you for ending the relationship.