I really think that I'm a horrible human being.
Are you sure? You really think you're a horrible human being?
Yes, I have fucked up a lot of my relationships
You should learn from your past mistakes and be able to grow as a person. It is not good to put your self down and dwell on the past.
I am a horrible person.
It's good you recognize all your faults, but that doesn't mean you need to keep beating yourself up from it! It would be great to pick up after all of this and try to become a better person by stopping all your wrong habits. You deserve to have a good relationship if you try.