Hi,
I am sorry but I am not sure of the issue.
Here is the code I added to your bp-custom.php

// For showing members of opposite gender.
function buddydev_exclude_same_gender_users( $args ) {

	if ( ! is_user_logged_in() ) {
		return $args;
	}

	$field_id = 3;// gender field.
	$data     = maybe_unserialize( BP_XProfile_ProfileData::get_value_byid( $field_id, get_current_user_id() ) );

	if ( empty( $data ) ) {
		return $args;
	}

	// we have two choices here.
	// show opposite gender or show all members who are not of same gender
	// I am going with opposite gender, feel free to adapt.
	$search = '';
	if ( 'Un Homme' == $data ) {
		$search = 'Une Femme';
	} elseif ( 'Une Femme' == $data ) {
		$search = 'Un Homme';
	}

	if ( empty( $search ) ) {
		return $args;
	}

	$args['xprofile_query'] = array(
		array(
			'field'   => $field_id, // field id or name.
			'value'   => $search,
			'compare' => '=',
		),
	);

	return $args;
}

add_filter( 'bp_after_has_members_parse_args', 'buddydev_exclude_same_gender_users' );

It looks into the field 3 3 of the logged in user, then checks for who should be shown.

Since I do not understand the language, The string values may be incorrect . Can you please check it and tell me if it is correct or not?

if ( 'Un Homme' == $data ) {
		$search = 'Une Femme';
	} elseif ( 'Une Femme' == $data ) {
		$search = 'Un Homme';
	}

Regards
Brajesh