Getting someone elses email

Ive used Gmail for years and have always been pleased. Only as of lately have I got a bit of concern. Someone else started using a very similar email address to me but it is just missing a (.) compared to mine. Even though it shows it as the other persons Im getting his emails sometimes and hes getting mine. Ive received sensitive job application emails for him and payment details and hes gotten the same on me. Weve even called each other since we had each others phone numbers yo check if it was fraud. This individually is a young adult and not wanting to change guys newly created email. Ive used my address for over a decade and dont want to change it. Please provide security fix for this!

Zjeepn82 about Gmail - Email by Google, v5.0.180225