I already created a widget and it's working fine. But there is no option to add widgets using page builder. What should I do?
Thanks
You have a couple of options. The simplest is using the Text content type to include the widget using the standard TinyMCE widget feature.
Your other option is to create a new content type that wraps your widget in a Page Builder content type. Our Products content type does exactly this, it's just an interface for the Catalog Product List widget.
products.xml contains a mass converter to create the widget directive:
view/adminhtml/pagebuilder/content_type/products.xml
<converters>
<converter component="Magento_PageBuilder/js/content-type/products/mass-converter/widget-directive" name="widget_directive">
<config>
<item name="html_variable" value="html"/>
</config>
</converter>
</converters>
You can refer to the detailed answer here.