Hi.
Make sure you don't look like anything before, don't use the same tattoos, skins - nothing that can be a resemblance. You would be surprised how often people go for it and don't even realize it. It's also possible that he uses your name to everyone he messages and just fishes for a response.
On the technical site..
You've got a new laptop - good! Now get rid of any IoT devices because they have crap security and could have been compromised - they can be used to gain foothold to your network and pivot further. Reset your router settings to default so any changes he has made are cleared. Standard DNS queries only include domain name but DoH/DoT(DNS over HTTPS/TLS) can include the full URL so if he has set his own DNS server in your router's settings, technically it's possible to find out your new name. For example, you have requested https://my.secondlife.com/myname and he can see "myname"
Another thing in your router is the option to set up a VPN which can act as a man-in-the-middle and allow him to intercept traffic. It's a stretch but still in the realm of possiblities. A reset will clear it. Call your ISP and ask tell if it's safe to reset it(might require configuration afterwards, also change the router's password) or maybe they can just come to replace it.
In the SL's viewer disable streaming music and media and only enable music when you are at some club.
In Media tab disable "play media attached to other avatars" - this can leak your IP address.
I don't think there's anything left you can do on the technical side of things.