Lied to by girlfriend. Should I break it off

So, I recently discovered my girlfriend lied to me about something pretty big. Basically she told me she broke up with her ex three years ago and yet I've seen posts on her Facebook which show that she was clearly still with him a year and a half ago. Plus a few other posts from about 6 months ago, along with things she has said that suggest they are still living together. Now, I am unsure what to think about this as I feel like I am unable to trust her after this. I have confronted her on some if the things she has she said and she has just said it's nothing and that she doesn't remember saying it. I am wondering what her reason for lying really is? I mean I don't think they are still together and she had no reason to lie about this at all, though I'm starting to wonder more and more about what else she potentially has lied about and whether she is still with him. She and the ex have a daughter together so I never suspected much when she mentioned that they are still friends as the kid comes first. I was hoping I could get some feedback on this and see what everyone else thinks about all this and what I should do next. I'm meeting her this weekend and I'm not planning to mention any of this till then. I could use the help as my mother is quite ill at the moment too so I have little time to think about this stuff myself and would really appreciate the help. Thanks in advance to everyone for the help.

I can'. It's killing me, I haven't slept all night and had to call in sick from work. If it was up to me I'd confront her today. I can't believe she would lie like that. It hurts like crazy.

You have a couple of days remaining till weekend, why don't you try and structure everything that bothers you? When you're hurt and desperately need to discuss it with your partner, it may come out as a mess. Break it down. Create a list. Have imaginary conversation with her, after all. From my personal opinion, when your partner starts lying to you, it means it's over. Maybe your case is different, but I completely share your thoughts on this one: 'what else she potentially has lied about?'. Relationships just don't work without trust.