In talking stage with male coworker who is away on vacation while I have to leave job suddenly. How do I leave my contact details for him?

I am in talking stage with my single male coworker since last month. He went on vacation last week and will be back next week. I am leaving the company today as something urgent has came up. We only had conversations on office chatting app and have developed a strong connection. Our interest in each other is clear.

Do I email to his office email id from my personal id and share my contact details? or should I send him text message/WhatsApp as I have his number from common work friends texting group?

Also, should I say that I enjoyed getting to know him and would like to keep talking and possibly meet at some point?

In talking stage with male coworker who is away on vacation while I have to leave job suddenly. How do I leave my contact details for him?
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