Hmm, I think if I were you I'd do:
1. Create a table called "Purchase Log"
2. Create a table called "Purchase Summary", make the primary field be the email of the purchaser and create a linked field to "Purchase Log"
3. In the Zap, make the trigger "New Purchase" and create a record in the "Purchase Log" table, and put the purchaser's email into the linked field to "Purchase Log"
4. Create lookup fields in "Purchase Summary" to display the purchaser's name, and whatever else you'd like to see
Now if "test@example.com" buys something, a new record gets created in "Purchase Log" with all the details of that purchase. Because we're pasting the email into the linked field to "Purchase Summary", a record will get created there too and you can view the relevant details via the lookup
If "test@example.com" buys something else, a new record gets created in "Purchase Log" that will get automatically linked to the record in "Purchase Summary". In "Purchase Summary", the lookup field to view the Events would now show you both of the events they purchased. You could make the "Events" field in "Purchase Log" be a single select field like you wanted for easier filtering too
Should work!
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You could also do this all within Zapier too! Using your existing base setup, you'd add a step in your Zap to look for a purchase record with the triggering purchase's email. Then have a conditional path where, if it finds something, just update it, but if it doesn't find something, create a new record
