Why does my girlfriend keep asking if I still like her?

So i work a lot but i still make time for my girlfriend. This was the reason i didn't wanna date anyone with how busy i was. So if i can't spend the day with her i'd spend the night at hers or she spends it at mine and that's the most time we spend together. Of course i still message her when i'm on a break since i have her schedule pretty much memorized. But whenever we're cuddling she just pops up the question, i don't know if she thinks because i'm only available to spend nights with her , she thinks that's it but i really like her honestly my first relationship in the past couple of years. I don't want her to think like that but no matter how i tell her i'm really into her there is this doubt she has i guess. I even asked if she thought i was playing her and she said she doesn't know, i don't want her to think like that. i absolutely adore i just need to let her know but i guess words aren't working. She has this look in her eye like she's bracing herself for when i say no when i might respond with a no which will never happen. I just hope she doesn't realize how much out of my league she is. So any ideas of how i can cement how much i like her into her head?

Why does my girlfriend keep asking if I still like her?
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