Should I call her or wait! Help?

I love a girl, with whom I had close relationship when we were together,(we we're staying in different room in same flat), she use to care for me, I care for her too. Now she went to her home, we often hv call which was called by me only. She don't call me herself, it took her time to reply meh. When I said if I am irritating or invading her personal space she denied n she said she will never feel irri or invading her personal life by me. Problem is that she use to tell me she will call me bck n which she don't. I know she has bf, bt she told me once she hardly trust anyone approaching her coz of her present relationship with his boyfriend. 

I truly loved her and I just want to hv just a minute or two of her talks. I don't want to mess up her relationship but am ready to accept her as my gf if she choose me later on n even marry her. I hv no gf. Now thing is that as she has promised to call me when I called her last time bt she didn't yet. Coz of this behaviour I hv not texted her n even not a call, but there is not a single moment I hvnt think of her. I missed her I just want to let her know unless if she call I will resume my txting n calling, am just trying to give her time n space. Am afraid if by doing so, am I not going lose her forever. Should I text or call, or shd I wait for her call or even short message. It's been near about 3- 4 days. 

Please take trouble to answer me am confused and my heart beat in unusual way by thinking of her. 

Thank you