I'm late to the game, but I've read through a lot of these and realized how sad they all are. Not to take away from anyone's hardship, but I wanted to share a somewhat "happier" story of mine to add some positivity to the heartache.
It's a little long, so I'll throw a tl;dr at the bottom.
Also, obligatory, this is a burner account for reasons that will be apparent shortly.
Basically, the hardest thing I ever had to say to someone was that I think we should breakup. It was a girl I absolutely adored, and we had been together for 2.5 years. We were engaged, too. And to sweeten the blow, it was my first actual girlfriend, so I had never broken up with anyone before. The problem was that for the last year and a half of the relationship, things slowly went downhill. It was subtle, but the effects definitely were felt. Initially, we clicked perfectly and were of the same religious background, so we were in sync in life, but as time went on, she abandoned what she claimed to believe and didn't share in the direction I thought the relationship was going, which is the same as we both upfront agreed upon in the beginning.
So anytime I pushed to continue in that direction, she resented me. When we first started dating, I was honest with her about a past pornography addiction, and she discreetly lost trust for me. As mistakes were made later, her history of cutting/depression exhibited itself again, and she very much clung to me for happiness, but as her distrust grew, she also held an overly tight grip. It was suffocating. She would constantly search my phone/computer to see what I had been doing or who I had been talking to, and any resistance I made meant I wasn't willing to earn her trust back.
During our relationship, I met my current best friend, an amazing dude, but from day one she had an "iffy" feeling about him, and didn't want me to really associate with him. As I continued to hangout with him against her wish of limitations, it eventually became an all-out ban on being friends with him at all, but given we weren't married at this point, and she couldn't give me a real reason of how he was a bad influence for me, I didn't feel right just cutting him off.
There's so much more I could explain that I don't think ever will grasp just how bad things were. It was an insanely mentally abusive relationship, and by the end of it, I was aware of the plethora of red flags, but for anyone who has been in this situation, the slow progression had ate away at my confidence. I was scared and didn't know what to do. It's a very real struggle, and any approach of the idea of taking a break or 'not being together' she would counter with threats of suicide. She twisted everything back at me and would explain how I was being abusive to her.. Overall, this time period was a literal nightmare. I both kept hoping we'd eventually work through the issues but also knew how bad things were getting. And she belittled me whenever I told her about asking people for advice. I was stuck, but I knew the relationship wasn't healthy for either of us, and she was still pushing for marriage.
Eventually through that same best friend and another really good friend of mine who I explained the issue to, they convinced me to go through with the severance. The second friend who I was talking to was especially fired up about some of the texts I showed her and overall situation, and she wouldn't let me back away from ending things.
So earlier this year on Good Friday, I finally said the hardest words I ever did. I sent her a text telling her I think we should break up. I realize I should have done it in person (and sooner), but I was too afraid. Since then, I've recovered immensely, and I am feeling so much better. Life is wonderful, and while I'm still sort of afraid of the idea of a new relationship, I really am looking forward to the future. It's still hard to remember, but I have a great group of friends to support me. She didn't freak out like I thought she would, but she still had a really hard time processing it, and I still keep tabs on her to see how she's doing. I realized I couldn't be the one to help her, but I still care about her, and she seems to be doing better. I for one am truly in a better place now.
If you got this far, thanks for taking the time to read this. I know I could have been brief, but I didn't want to shy away from the reality of it all. If you have any questions, feel free to ask. I'm happy to share.
tl;dr I was in an incredibly mentally abusive relationship, and broken to the point of being afraid to break up. But I finally told her we need to end it, and since then I have been the best I've been in years. Life is good.