If you need to share a secret with a friend, you shouldn't use email, SMS, or online chat. Email can be read and changed in transit. Text messages may not be secured end-to-end. Chat logs wait in the cloud for a hacker to riffle through your life.
Email a SneakyNote instead.
A SneakyNote is an encrypted message with a unique link that looks like:
The link can only be accessed once, so you can send it to your friend however you like.
Once they read it, no-one else can. Ever.