Bullsh!t... You're attached to her and you can't just change that by telling yourself what you said in your last post. Don't try to kid yourself and act tough... You are attached to her and it would hurt you if she cheated on you. That's the truth and it's bullsh!t to act like it's not the truth...
You can't change those feelings, man. You DO have an emotional connection to her and it DOES hurt if she cheats on you. FACTS which you can't change.
However, you can change the way you respond to the situation, you do have control over that. So if her behavior seems suspicious, keep an eye out and be on your guard! Stay calm and level-headed, though... You don't want to appear like the insecure, jaleous, suspicious boyfriend.
You could just ask her in a casual way: "So babe, which city are you going shopping anyway?" Or maybe tell her "How about going shopping together that day, it'll be fun!" See how she responds to questions like that... Does she hesitate in her answers? Does she need to think before she answers? Does she act a bit nervous? Do her answers seem contradicting? (ask her something and ask the the same question 1 or 2 days later).
If you ask me, her behavior does seem suspicious... She didn't even give a reason why she wants to go alone, right? That in itself is suspicious... Fvck thinking you are overreacting! Why would she insist on going alone and not even give a reason for it? Also, the way she communicated this is suspicious. I would expect her to say something like "would you mind if I go shopping without you?" or "I think I might go shopping alone this weekend, hope you don't mind?" But instead, she just TELLS you she's going alone, like you can't disagree and it's not open for debate. Why would she need to communicate it in such a manner? That's the way people communicate when they want to do something which is not allowed... It's the way I would communicate when I know I'm about to do something which the other person doesn't want me to and I've decided to do it ANYWAY.
It's as if she was AFRAID that you would say "no, you cannot go" and wanted to prevent you from saying no. Well, is shopping on her own something you would not allow and say "no" to? Is there a reason for her to try and prevent this, communicating in such a strict manner which prevents you from protesting? Is her going shopping on her own something harmless which you would be perfectly okay with? If so, then why the fvck did she feel the need to communicate it in such a manner, TELLING it, leaving you no room to go against her decision? And why the fvck did she look for a reaction? (you did sense that, don't tell yourself you didn't, you DID! Trust yourself...) It sounds like there was tension around her when she told you this, right? Why would there be? If it's no big deal, something innocent, then why was there tension surrounding her?
I think you should be on your guerd here, man.
If a woman wants to cheat on her man, this would be a pretty good "excuse" to create the opportunity to do so. And you wouldn't be the first guy who got cheated on in a situation like this, man.... Sh!t, there's hundreds of stories like this where the b!tch DID cheat on a guy! We all know the hypergamous nature of women, this forum is full of it. Now here is a woman who acts strange, suspicious and out of character...but you should just ignore it, don't worry and simply trust that all is well?
Fvck that sh!t, I would investigate this situation very carefully and see if there are signs that point to her being unfaithful to you. You have good reason to do so, her behavior is out of the ordinary.... BUT AGAIN, do it with a calm and level-headed attitude!! Don't give her the idea that you're suspicious, just act casual and do your "research" in such a way that she doesn't notice it! Be smart about it!