How can we know that a girl has been pregnant before?
My Girl friend having an stretch marks on her stomach and her breast are also too loose,
She also had an surgery mark below her stomach she say's that she had and cyst operation earlier so
Is it like that or she is hiding her previous pregnancy from me?

Weight gain and loss can cause stretch marks. Cyst surgery can cause the scar. Why not believe her?

You can only trust that she is telling the truth.

As has been noted above, weight gain and loss can cause stretch marks and "loose" breasts. Surgery to remove cysts can leave the scar that she has.

And why does this matter to you?

I don't know what you consider "loose" breasts but maybe you just haven't seen enough of them to know that breasts come in a variety of shapes and sizes.

I had stretch marks and a huge "c-section" scar from cancer surgery 11 years before I had my first child. These things happen. You should either trust your girlfriend or get out of the relationship and let her move on.

Yes, you have no business being with this girl if you can't believe and trust her. If she had posted this we would have told her to leave this guy since he sounds too controlling and demanding.

First if she had a child, it does not matter, that would be the past before you meet. Next if you can't trust her you don't need to be with her.