About to do long distance, and I’m going through it

Hey guys! I’ve always used this sub for support and would appreciate if you give some advice today, even if it’s tough love.

Long story short, my boyfriend and I are about to do long distance (I’m in Canada, he’ll be in Europe) and I’m starting to spiral away. I went to therapy yesterday and I’ve been crying non stop. I’m terribly afraid of being alone, and I know that being alone doesn’t mean being lonely, but it’s hard for me to assimilate that. Any advice for how to handle this?

Mind you, we’ve been living together for the last 4 years so it will be a major change. A lot of my friends are friends I’ve made through him, which unfortunately have also gone (will also go) back to Europe. I’m trying my best effort to join meetup events but I also know this will take time, and I’m scared of being alone.

We met a guy last week, for a 3some albeit, and the vibes were great. And now I’m also “platonically” attached to him (I couldn’t care less about the sex). I’ve seen him once more and my bf has seen him 3 times now - all in a non-sexual environment (drinks at a bar, pride, etc). My head is now spiraling as I would love this to be a long-term friendship, so now I’m overly dissecting any message he sends out. Also, he met my bf first (they hooked up first, they’re both French too) so clearly they’re closer. So now I’m doubting my social skills - I’m scared that once my bf leaves, he won’t be interested in having a friendship with me.

Apologies if this is all over the place, but would love some advice! How to handle long distance, how to make new friends, how to stop over analyzing/overthinking everything.