Enclosed please find a sample template demonstrating how to copy a repeating table values merged into a multi-line textbox with a rule
Having filled your Basic view as shown below

upon pressing Advanced button, the Advanced view (filled with a rule) shows:
The rule "Copy repeatable table values to textbox" was added to Advanced button click even handler

Note that XPath of rule was created by simply clicking on Infopath GUI, codelessly:
- eval(eval(group2; 'concat(my:Products, ";", my:field2, @crlf)'); "..")
which later appears as
eval(eval(group2; 'concat(my:Products, ";", my:field2, xdXDocument:GetDOM("characters")/characters/@crlf)'); "..")
You could edit it in order to merge values in different format
I used "double eval" explained in
Inserting line break @crlf into a text box is explained in:
Also, I enabled multi-line in text-box properties