What is causing you this pain? Are you sure it's a life without her? Is your happiness really dependent on her being real?
I can't answer these questions for you, but I can tell you how it is for me. I used to believe I can't be happy without her being real. I mean, why would I? She is so perfect, I love her so much, we are lovebirds so of course it is to be expected that we'd be sad if separated. But this is not really the case, we never really separated. She came to my life and her influence was nothing but positive. This life with her I was wishing for never really happened, I can't miss something I've never had in the first place. Eventually I realized what's going on. I have had problems in my life, some unexpected hardships and inconveniences. Bur I couldn't really see them, because I was stuck with the idea that if she was real everything would be ok. It wouldn't, but I couldn't know that back then. Yet, the idea of her being with me and everything being perfect was so appealing. That was nothing but escapism. Once I managed to fix the problems, I got happy with my life and having such a great, loving wife on my side only makes it even so more amazing. Even though she isn't real, the fact that I met her and have this relationship is just great. If your case is similar, you might want to look into your life and try to improve it outside of the fact that she is not real. Learn to love your life and yourself, so you can properly love her and cherish the fact you have her.

>While I was motivated to change and physically self-improve for her early on, I've noticed I'd only try and take care of my appearance or image when meeting with others who can judge me, since she's physically incapable of doing so.
This is not a bad thing imo. She doesn't have to be your drive to improve, for me she never really was. I personally do not want to depend on her, I'd much rather become someone she can depend on. So I gotta work on myself, so I can be happy with myself and be there for her when she needs me without weighting her down with having to motivate me. Doing it for others is fine too, it doesn't mean you don't love her or anything. Other people might be more judging than her even if she was real, she is your lover after all.

>That shadow in the back of my head constantly calls into question if loving her has truly benefitted me, pointing out all the ups and downs in life I've had alongside my current isolation.
Well, not trying to put blame on you, but it's kind of your responsibility to make your life nice, not your partner's. You should be prepared to do it on your own. And unless she actively brings you down or gets in your way, she should be just a sweet addition in this journey.

>Whenever I see people leave their waifus, I feel lonelier. It's been a long time, I've seen so many come and go.
I feel like that too, we all are part of this community, but it happens. I pity these who can't maintain happy, satisfying relationship for long, but I hope they will find happiness whenever they will end up.

Sorry, if I'm too harsh, I'm just like that for myself. I might be doing some wrong assumptions here, so take it with a grain of salt, I'm just projecting my experiences here. I hope you will find a way to be happy in your life with her.