I'm going to block my ex after he showed signs of suicidal thoughts
Are you serious? Why would you block him when he's vulnerable?
I already felt like I wanted to break off our friendship after he slept around after we broke up
It's understandable that you want to distance yourself from your ex, but first make sure he is getting help for his depression. You would feel really bad if you just blocked him and then found out he committed suicide.
I didn't think about that. Even though it's my fault for breaking up with him. I should care about someone's life and friendship more than myself.
It's alright, the situation seems very stressful and you seem to handle it well. I'm sure your ex will appreciate you trying to help save his life. Bygones can be bygones, and their life is worth more than a breakup.