I can relate to this, I'm not much for attaching to people but I have this time and it's very intense and the fear of him leaving is constantly there and I don't even have a reason to really think it like you.. he has to reassure me often and I refuse to leave weekly and go longer between etc. he knows I'm strongly attached.

I nearly had a meltdown when he was on a weekend trip in another state, didn't even effect my sessions but I was terrified he would die or just never come back. I was sick all weekend, it was awful, so I completely get it

I also wont see any other T so I get that

I've been honest about googling my T but he has also told me I could. I guess, you could always just say "I'm worried about you leaving me, is there any trips or any big reasons you would need to be away in the next few months?" I literally ask this every month or so.

Good luck. It's awful