God this is a doozy. I swear my life feels like a movie right now. Sorry for the weird formatting, I'm on mobile and this is my first time posting on a sub like this.

I (28M) am planning on proposing to my girlfriend of 3 years (26F). Now, I suck at picking out jewelry. Im the type of guy that doesn't see a problem with heart shaped jewelry (seriously why is it considered so ugly?) so every time I want to buy something for my girl, I usually consult one of our mutual friends. My girl's best friends are all friends with me as well and we all get along well, so asking them for help picking out jewelry is something I'm used to.

When it came time to pick out a ring, I consulted my girlfriends best friend Justine (fake name). Justine and I are quite close and she knows my girlfriend better than anyone, including me. So, when my girlfriend when out to visit her sister and baby nephew, I invited Justine over to the house to help pick out a ring.

Justine and I looked through a few catalogues, but decided it was a dead end and it would be better to go to professionals at a jewelry store. However, I didn't know when my girlfriend would be coming home, so Justine and I thought of a clever text to gauge how much time we had. I asked her when she'd be coming home, as I was ordering takeout and wanted to know when to tell them to have the food ready by.

She responded by saying it would be a few hours, she met up with Justine to go shopping. Now, obviously this took me by surprise since Justine was standing inside my house. I showed Justine the text, and she looked as confused as I was.

It isn't out of the ordinary for my girlfriend to meet up with people out of the blue like that for shopping, lunch, etc. She's a very spontaneous person and loves making plans on the fly. So ordinarily, I would have believed this text in a heartbeat. However, obviously this had to be a lie.

When she came home she acted completely normal, and I played along but it's been really hard to act like everything's fine. We got takeout, ate together, and cuddled on the couch after. So far she's caught on a little that somethings upsetting me, but I just can't tell her what. Looking at her kills me.

I don't know what to do. My girlfriend and I have zero trust issues and we tell each other everything, so this lie is killing me. I want to ask her about it so bad, but if I tell her I knew she was lying, I'd have to explain why, and I really don't want to do that. What do I do? I know she lied to me but I don't know how to confront her about it. Should I just forget it? This won't stop gnawing at me. Please help!

Edit: I'm sorry for the lack of responses, it's been a hectic day and there's a lot of comments. Thank you to everyone who has commented so far, I appreciate them all!!

Edit #2: sorry again for the lack of responses, guys. It's really been a crazy day. My parents are moving and I've been helping them. Also, I've never experienced this many comments on a post in my life!! I am going to talk to her tonight once we're both finally settled in after such a busy day, and I will update tomorrow.