Yes, P'Kras is her bf but she did not love him, you can see that Sitang won't contact him if it's not necessary.Plerng and Sitang bickering is so darn cute. Is Kras Sitang BF ?? all along I thought he was just a friend or someone who worked with her.
And why Kras is being her bf then you need see it in future ep. It's related to past life, Pakboon made Sitang saw her Duangkae life and make it seem like she and Kras are husband and wife.
In the end of ep 1, when Plerng asked Sitang who is her previous life, Sitang lied that she hasn't let Pakboon do that with her, i think because she still have doubts about what Pakboon let her saw.