How can I let my partner have friends?

I know a lot of people with BPD deal with being controlling and jealous so Im seeking some help here. I've been talking with this guy for around 9 months and 3 days ago we made it official. During that time when we were talking, I made it obvious I didn't want him having any friends that weren't me, and he had like 3, while I only had him. And during the time we've been together hes made friends and left some for me. I really don't want him leaving other people. I want him to have a regular relationship with me while also having friends, but It feels genuinely impossible. We've already gotten into fights about this multiple times.

I really want our relationship to last (considering this is my first), I've gone to therapy multiple times trying to treat this but nothing ever changes D': But I hope to find some way to cope :)