Privacy/Security Advice: An online friend found my WhatsApp number and family details. How can I check if my devices are compromised?

Hey everyone, my name is Ste and I really need some advice from cybersecurity experts. I’m pretty new to Reddit, but I figured this would be the best place to ask for help. I have a degree in Software Development (DS), but I don't work in the field. Having that background means I'm not completely tech-illiterate, but when it comes to cybersecurity, I know next to nothing.

Here’s what’s going on: I’ve had an online friend for a while now. Recently, he brought up some personal information about me that I never shared with him (like the names of some of my relatives). It annoyed me, but I didn’t panic because I assumed he just stalked my social media.

However, today he messaged me on WhatsApp. I have never given him my phone number, and I am certain it isn't publicly available anywhere.

I want to know how I can verify if my phone and computer are truly secure. A while ago, my computer was hacked/compromised. I did everything I could at the time to clean it up, but this new situation has triggered my paranoia, and I’m terrified that I might be monitored again. Can anyone point me in the right direction?