Should I Trust Her?

I am having some weird feeling with this relationship that I have with Ms D. I felt like as if she is trying to hide something from me.

And now, she openly sms her other friends in front of me and will get agitated when I asked her who is the person she is sms-ing. I have every right to ask that question now, do I?

We have been in this relationship for almost 4 years but I still have a big problem to trust every word that she said to me.

And she seems to have a better relationship with her foster brother than me. Well, I am sure you would be upset too if your girlfriend is busy sms-ing another guy that she call her foster brother when she is hanging out with you, don't you?

I hate myself so much for giving her so many chances.