I regret ever allowing my mental health to plummet to a degree where I was alienating my friends and significant others. I should have sought treatment and attempted self control.
I also regret ever dating my ex... I only started dating him because I was scared that he would successfully kill himself. I never really liked him, but was scared to leave him because I knew he had a history of attempted suicide, he was incredibly unstable, and he had seriously hurt other people before... in a physical way... fatally... (DO NOT DATE A MURDERER. EVER.)
When I eventually broke up with him, he tried to manipulate me by attempting suicide so I would take him back. It was almost a good thing that he found out I cheated on him just because it made him finally leave me alone. Except, being the crazy guy that he was, he used the fact that I cheated on him as a way to try and deface me, ruin my reputation, and make friends hate me. He succeeded with a few people that were very good friends of mine. Granted, his being a total and complete dick doesn't completely justify my cheating on him, but I'm still sick of people telling me that I deserve the defacement and demonization because I cheated on him. I was cheated on by two people, and remained completely civil in both cases.
Moral of the story: seek stability, don't date someone just because you feel sorry for them, and DO NOT DATE CRAZY PEOPLE (I don't refer to mentally ill, I mean people who will use suicide as a tool for manipulation).