Long Distance Relationship Advice

I have autism and have been with my partner for the last two years, though she lives in Australia and I live in the UK. It's been so difficult anytime we split apart and I'm at a loss on how to cope with it each time, especially adjusting to the change. I get so used to having her with me, and so comforted in her presence, that I don't remember how to exist when she's gone. I've had issues with anxiety and depression for over a decade and it's always been constant, but with my partner I feel I'm actually capable of handling it and being happy. When she goes, I feel like I'm back to nothing and just waiting until I can see her again. 

I know she isn't a solution to my problems, but she helps me feel more able to tackle them and, above all, comfortable being myself around her. I try to focus on enjoying the time I have with her when we visit but by the time it's over, it feels like it went by so quickly and seeing her again will always be so far away given the cost of the flights. I'm tired of feeling awful and I think I deserve to be happy with her, but the waiting is killing me, especially the longer we're together. After my depression being so constant for so long, it feels like I've finally found something that will help and it's just out of my reach. 

I've always been good with things being out of my control, knowing there'll always be some way to work things out, but in this case there's just nothing I can do but wait. I know that it'll work out eventually and there'll be a day where we can be together, but I don't know how to not fall apart in the meantime. Neurotypical people tend to remind me that I'll see her again and can still call her, which should be comforting, but it just doesn't solve how I feel right now. I wanted to see if anyone else has been in a similar situation and if there's any advice out there on handling the separation anxiety I keep feeling. I'm so scared to go to bed because I wake up anxious or ill knowing that I'm alone again, so any recommendations for passing out would also be appreciated.