how does the first amendment coexist with defamation suits?

What happens is if you somehow destroy someone's life with slander you basically have to compensate that person if they sue you and win

Some BS Supreme Court ruling.

Slander is verbal; libel and defamation are written. The amendment includes access to a "free" press. That the press is longer free is legally irrelevant. That is how the first amendment and defamation/slander lawsuits can coexist at the same time.

I am not a lawyer or a paralegal.

It's only slander or libel if it's false. That's the line. It's not much, but it generally works.

if you're talking about Trump saying he will sue for slander, he can't, a president can not sue for slander

Slander causes harm financially, or sometimes physically, like with Antifa doxxing dissenters to violently attack them.

Libel and slander are not covered by the 1st Amendment. 'Defamation' is not really a matter of law. 'He said something bad about me' is not a legal matter. If someone slanders (spoken) or libels (written) you, you can sue them. However, if it's TRUE, it's not slander or libel.

The government doesn't stop you from being liable for your actions.