Facing problem with tax_query results

I need to get search results for posts on the basis of post-category(must) and posts-tags(optional).
The process is like:

1. search for a string e.g. "bananas"
2. the category is always static
3. need to check banana term in post-title, descriptions and in post-tags

Currently I am using multiple tax_query but it shows results only in (tags) or in (post-title, descriptions). But I need the combined results.

Here is my code:

    $catgory = 'case-definitions';
    $terms = explode(' ', $_GET['s']);
    $args = array(
        's' => $_GET['s'],
        'posts_per_page' => -1,
        'post_type' => 'post',
        'order'  => 'DESC',
        'tax_query' => array(
            'relation' => 'OR',
            array(
                'relation' => 'AND',
                array(
                    'taxonomy' => 'category', 
                    'field' => 'slug',
                    'terms' => $catgory
                ),
                array(
                    'taxonomy' => 'post_tag',
                    'field' => 'name',
                    'terms' => $terms
                )
            ),
            array(
                'taxonomy' => 'category', 
                'field' => 'slug',
                'terms' => $catgory
            ),
        )
    );

Can anyone please help me out to correct me? Much appreciated!