I've loved my girlfriend for over 2 years, and I still do. But now she lyed to me about something pretty big. Should I break up with her?

No, I don't think that 你 should break up with her. I know that this is big news to 你 -- and it's natural to feel this sort of "betrayal", being as she didn't tell 你 -- but what she's dealing with is most likely psychological. I know that 你 think she shouldn't be afraid of you, but it's harder to get rid of something such as this. If she's been abused, it gets stuck within the subconscious; she's afraid of it happening again. 你 have to assure her that you're a different person, and that 你 would never do that. Gain a lot of trust from her, even if you've been together for two years.

In her fears lies the answer to why she hid those things from you. Her insecurities -- which ties in with the subconscious and psychological problems -- made her stay quiet about the whole thing. And when there's new relationships made, it's usually a smarter idea to hold back talking about an ex-boyfriend (from what I've read at one point, anyway). I may not have ever gone out with someone, but I can easily understand feelings.

It's going to be hard to decide what to do; I understand that from 你 as well. If I were a guy and my girlfriend told me that, I'd be shocked as well. But would I break up with her? Most likely not, as she had a reason to why she withheld all of this info from me. She didn't mean any harm, but possibly that, since you've been together so long, she can trust 你 when telling 你 her secrets. 你 can't always know everything about someone, as 你 learn something new everyday, but she's trying to make that start.

I would tell 你 to trust her (and it would be my recommendation, of course), but that kind of thing is for 你 to decide. All humans have different minds, so we shouldn't have the right to tell someone what they should think. I hope that this helps in some way, and good luck.

Nah, don't break up with her. What 你 really need to do is talk to her about it, I would've hidden that from my boyfriend to. She probally just didnt want 你 to think of her badly. If 你 爱情 her, and she loves you, 你 can both still be together. Sit her down and makes sure there's no 更多 secrets from either one of you. Maybe tell her some of your thoughts 或者 secrets. Once she sees 你 trust her, she'll trust you.

Whether 你 break up with her 或者 not is up to 你 alone to decide. But 你 have to think about this properly. You're feeling angry and sad she didn't think she could trust you, and 你 in turn feel like 你 can't trust her now, that everything out of her mouth will spout 更多 lies and shock. Understandable.
But as Chibi-baka 说 (i seem to be saying that a lot lately), it's a very touchy subject to breach, and obviously for her to feel so frightened and fearful of 你 that she couldn't be honest in the first place, makes me think she has been in an abusive relationship and therefore has been tarred with a brush that will stay with her for the rest of her life. Her trust in men has hit rock bottom, and 你 alone have 给 her a glimpse that not all men are bad. That is why she has decided to come clean.
When a person is in a abusive relationship, the victim (your girlfriend) can suffer horrendous hardships and due to the psychological damage 给 由 the abuser, can begin to think it is the victims fault the abuser is 表演 this way, because that is what they are told. 'You made me do this, now see what 你 made me do, it's your fault' etc. Enough of that can turn any resolve and 你 start to believe it yourself.
Depending on your age it may not have been her choice about the children she had. Her parents, 或者 even her ex may have forced her into giving her children away. It could have been due to the circumstances she was in. What mother would keep her child knowing what her boyfriend was like, what torture he can put her through, and who's to say he won't do that to the children? She may have had them adopted for their safety, that she was mentally, physically 或者 financially unable to care for them properly, 或者 she may have found the idea of motherhood too traumatic to deal with at a young age in a relationship that clearly made her unhappy. All are good reasons to save a child in any way possible.
It's not strange that she doesn't know her children's names 或者 how they are. Once the adoption process has been completed she had forfieted all rights of her children away. She no longer has any legal background of their up-bringing. She would be unallowed to have contact with them, she wouldn't be allowed to have any photographs of them 或者 any information on who the childrens new parents are 或者 where they live. It is all done to protect the child.
Giving away your child is the hardest thing to do, even when 你 know it's the right thing to do. Just imagine how your girlfriend feels, knowing she has three children out in the world somewhere, who may never know who she is 或者 where they came from, 或者 why their mother gave them up. Your girlfriend will be thinking - one day, will they try and find me. Will they want to know who their father is, and what will i tell them? Will they be angry 或者 understanding?
That alone can be mental torture. Please see comments.

Sounds like your girlfriend really likes you.You guys still have feeling for each other,right?
maybe when she lied she thought that 你 would be mad at her and 你 would want to end the relationship.Plus,I dont think she would have wanted to keep the whole thing a secret if it werent for that ex of hers threatening her.
So,overall, I'd say 你 need to have a good talk with her in person.

Don't do it