What can I do/try to make my girlfriend seem more real?

So I am in my first relationship, we've been dating for a little over 10 months. She is absolutely perfect for me, I keep telling her that she is literally an unbelievable dream-girl... because she really is. But I am now 20 years old, and for my entire life that I can remember I have been severely depressed, stuck inside my own head all the time, and I have always been very detached from the rest of the world and other people.

So, when I'm with my gf she doesn't really feel real in a sense. I mean, I'll walk around and see other people and interact with them, and it feels like I am actually engaging real people and I feel like they are actually there and conversing and interacting with me. But when I talk to my girlfriend, it feels like there ISN'T someone there... like I'm just inside my own head almost imagining our conversation or our sex or whatever we're doing. In sex, she can say and do the exact same things to me that anyone else can do, but for some reason they just don't seem that arousing or like they're truly happening to me... I imagine its not like it would be with someone who I saw as 'real'.

Anyway, I'm sure this is kind of weird or difficult to follow... but I really would LOVE any help. Write as much as you can/want, I really love her and I just know that if I could feel more like she's really there then literally everything we do would get SO much better. Thank you. (10 pts. for best answer as some incentive)