Am I overreacting, or is this a valid thing to be hurt by? [22M] [20F]

TLDR: I’m looking for honest opinions because I’m struggling to separate my emotions from reality.

My girlfriend and I have been together for a few months. We love each other, have talked about engagement, met each other’s close family and friends, and we’re both serious about the relationship. We’re also both Christians, and faith is an important part of our relationship. So, um. There we go. She told me that the day before she masturbated because “you weren’t here.”

I didn’t get angry, but it really hurt me. For me, when I’m in a committed relationship, I don’t even think about masturbating. My mindset is that if I have the woman I love, I’d rather wait until we’re together again. So when she told me that, my mind immediately went to, “Am I not worth waiting for?”

She told me I was overreacting, but that’s honestly not what I’m feeling. I’m not trying to control her or shame her. I’m just hurt because, in my head, intimacy is something that belongs to us, even if we’re apart for a while.
I’m genuinely trying to understand whether this is just a difference in values around sexuality, or if my feelings are understandable.

Has anyone else experienced something similar? How would you interpret this if you were in my position? Ps, I love her so much, and I try my best to treat her well as much as I can.