Mazal tov! May you and your future spouse share much happiness and success together!
One reason for breaking a glass under the chupa is in order to remember the Temple and the glory of Jerusalem during that era, as it says in the verses in Psalm 137:
“If I forget you, O Jerusalem, let my right hand forget its skill. Let my tongue adhere to my palate if I fail to recall you, if I fail to elevate Jerusalem above my foremost joy.”
So, even at a time of "foremost joy," we smash a glass in order to remember the destruction of the Temple.
Another reason is based on the Talmud in Tractate Berachot that says: "The Torah says, 'Serve God with awe and rejoice with trembling'... Rav Ashi made a wedding for his son. When he saw that the Rabbis were getting carried away in their rejoicing, he brought out a crystal glass and broke it in front of them, and they became subdued."
Many commentaries state that this is the source for the breaking of a glass at a wedding. We learn from this that even at an occasion of great rejoicing, one must take measures to ensure that the celebration remains within the bounds of propriety.
Some people jokingly say that the husband stomps his foot on the glass under at the wedding since it’s the last time he will “put his foot down”.
