דַּרְכֵי צִיּוֹן אֲבֵלוֹת מִבְּלִי בָּאֵי מוֹעֵד (Eicha 1:4). But first be double-sure that you aren’t depressive. In that case, you have to spend all your time and Kochos on being super-happy and happy and more-happy. Hashem understands, and He will have more nachas from you working on Simcha instead of crying for the Bais Hamikdash.
But when you do cry, remember the beautiful Mizbeach and Shulchan and Menorah, and the sweet smelling Mizbeach HaKetores and those lightening-speed holy Cohanei Hashem, and the incredible “Mar’eh Cohen” after the Cohen Gadol left the Kodesh HaKodoshim on Yom Kippur.
Cry when you think of Simchas Bais HaSho'eva, and everyone crowding on Erev Pesach with their tiny lambs. Remember the excitement and the music of: הַבָאַת בִּיכּוּרִים (bringing Bikkurim; the massive parade of people who were coming to the Bais Hamikdash to thank Hashem with Bikkurim), and don’t forget the Simcha of being Oleh Regel, and proclaiming: "שָׂמַחְתִּי בְּאֹמְרִים לִי בֵּית ה' נֵלֵךְ" How I rejoice when told we will go to the house of Hashem. "עֹמְדוֹת הָיוּ רַגְלֵינוּ בִּשְׁעָרַיִךְ יְרוּשָׁלָיִם" Our feet were literally standing within your gates, Yerushalayim.
You can go meshuga over the loss of the incredible Simcha which we don’t even understand. Hashem’s own house! It’s all gone! And plenty of Simcha disappeared from the beautiful world. Instead, we have all kinds of pain and weaknesses (in Ruchaniyus and in Gashmiyus). Chazal say: יָרְדָה חוּלְשָׁה לָעוֹלָם (Megilla 21a) people became weaker.
