My (21F) girlfriend (21F) is still hung up on her ex

Me and my girlfriend have been together 11 months and we’re pretty serious. We’re moving in together and we talk about our future’s often. Up until this point, my girlfriend has seemed totally committed to me and our life. in fact she’s been a perfect girlfriend, constantly giving me affection and telling me how happy i make her and how she thinks i’m the one and how she’d be stupid to mess things up with me. I have had no reason to believe anything negative, and I was fully assured that she was deeply in love with me.

Recently she’d been journalling a lot, we journal together sometimes so it’s something l’m aware of but haven’t really asked about. Earlier today while I was cleaning, I saw her journal was left out on the desk so i went to put it away. When I picked it up I saw my name on the page and I know this wasn’t good of me to do but I got curious and ended up reading her latest entry.
She talked about how she’s been thinking of her ex a lot lately and she wrote that she’s ‘madly in love with her’ She hasn’t had any contact or anything like that, and they will never get back together so it’s purely just thoughts right now but I honestly felt so betrayed reading that. she also wrote that her ex treated her really badly and didn’t deserve her but she just couldn’t stop thinking about her and that it made her angry. I get that she can’t help how she thinks and feels but I feel so stupid because now i feel like a rebound or a distraction. It feels like everything she said to me was a lite and she’s just been thinking about someone else the entire time.

It just hurts a lot because this is something we’ve talked about before because it’s an insecurity of mine. I’ve been cheated on with an ex so it hits close to home.She knows about this and there’s been issues with her ex in the past which is why it hurts even more now. she told me over and over again that she had no feelings for her ex at all, she promised me that she doesn’t even think of her and that she is so madly in love with me. the fact that she’s just lied to my face about this is unbearable.

I don’t want to be the other woman or the placeholder whilst she tries to get over her ex. I think it’s shitty that she pursued something with me whilst still being hung up on her ex. But at the same time she wrote that she’s really happy with me and I just don’t know what to think or do.

I had a conversation with her, without telling her about me reading her diary because i feel really guilty about that, where I guess i just asked for reassurance and told her that I felt like she didn’t love me. she’s been reassuring since then and tells me non stop that she’s in love with me, she tells me that she wants me and basically everything that i want to hear. it feels so empty though because I can’t get what I read out of my mind. I can’t just believe what she’s saying because now i feel like she’s lying to me. I just feel so stupid and so used and so upset that I’ve given her my heart and the whole time she’s been comparing me to her ex. i just want to be loved and her number one and it feels like my entire life is falling apart right now.

I can’t ask her about the ex business because I don’t want her to know that I read her diary, but apart from that I’m still really confused. Do you think she actually means it? I’m stuck because I love her and don’t want to leave at all but at the same time I feel like I would be letting myself down by being stupid and staying with someone who doesn’t value me. Please give me some advice on whether I should stay and give her the benefit of the doubt or just leave.

For context, her and her ex were together for just over a year and broke up a month before me and my girlfriend started talking. They had a really toxic relationship and her ex treated her very badly. They are no contact and my girlfriend has her blocked on everything. Her ex is also married now and very much does not like my girlfriend so I know for a fact that there’s no contact or chance of anything ever happening. It’s honestly just the fact that she thinks these things that’s bothering me. It’s hard to be in a relationship with someone when you know that they aren’t fully committed to you, regardless of the fact that she hasn’t cheated on me, I still feel betrayed.