Visiting Webpage ONLY after another page was visited. Possible?

You could set a cookie upon contact form submission, then check for the cookie on /page2. If it is not found, wp_safe_redirect() back to /page1.

Setting a cookie – You will need to hook into Contact Form 7’s submission – look into their documentation:

<?php
setcookie( 'my_cookies_name', true, 0 ); // This cookie will expire after the session
?>

Retreiving the cookie (on /page2‘s php template:

<?php
if( is_page('page2') ) {
    // Because the value is set to true, you can just check for the value in if()
    if( ! $_COOKIE['my_cookies_name'] ) {
        // cookie isn't found, redirect back
        wp_safe_redirect( site_url('/page1') );
    }
}
?>