No. The first one has strange grammar, but it has a very different meaning from sentence 2.
He really cannot be trusted= you should not trust him. He will betray you.
He's deeply insecure= he is always very nervous, and afraid that other people think bad things about him. He doesn't have much self-confidence or self-esteem.
Insecure people are sometimes very trustworthy: they work hard to prove that other people should trust them.