Android aar library doesn't contain dependencies

what should i do to make my main project see my library's third party dependencies?

The aar file doesn't contain the transitive dependencies and doesn't have a pom file which describes the dependencies used by the module.

It means that, if you are importing a aar file using a flatDir repository you have to specify the dependencies also in your project.

You should use a maven repository, private or public, to avoid the issue.
In this case, gradle downloads the dependencies using the pom file which will contains the dependencies list.