Me [27 M] find out my gf [27 F] (6months), texting other guys

So few days ago after lovely day with my gf, she gave me her laptop to clear it up. Also at this day she said, she has a problem to solve, when i ask what heppen she said, she figure it out herself.

At home I start checking her laptop, after i done i check if everything is ok and open web browser.... and then 4 last closed tabs pop out, one of them was dating website. I saw this and i couldn't stop myself to check it out.... I found out my gf texting other guys daily and sometimes going out with them for coffee. I read a lot conversations in her profile, most friendly talks, few ends with skype calls! and going for a coffee together, she never mentioned he has a bf.

Now i don't know what to think and what to do. WE spent great time together, i was thinking we are going somwhere... WHat should i do? I can't tell her i read her private conversations on her dating profile... I'm so lost, so sad, i love her.

Sorry for patato english

tl;dr: I found out my GF using dating website to meet new guys.