彼を信じるとはばかなことをしたもんだな、君も。の英語

You should have known better than to trust him.

It was stupid of you to believe in him.

It is stupid of you to believe in him.

It was misguided of you [＝You were misguided] to trust him.

It's silly of you to trust him.＝You're silly to trust him.

When you hear his sermons, you will be able to believe, too

It's silly of you to believe him.

You probably cannot believe him.

A word from you will cheer him up.

Don't believe his story [what he says]; he's just pulling your leg.

You had better not believe him.

Don't trust him no matter what he says.

I can assure you that he's sincere.

Whatever you said to him made him feel better.

I can assure you of his sincerity.

It's a pity that you trust him more than me.

He said so to reassure you.

You should've taken his advice.

You should have accepted his advice.

It is silly of you to trust them.

He was saying hi to you.

He was saying his regards to you.

He said hi to you.

He said to give his regards to you.

Don't put much confidence in him.

“So you don't trust him?"—“No, definitely not [Definitely not]!"

Why don't you try asking him about that too?

I want you to tell that to him.

You should pay more attention to what he says.

You should have told him the truth.