I feel low

Just lately, my friend has been acting weird. She only seems to want to meet me if my boyfriend is there, has cancelled plans with me at the last minute about 6 times in the last 2 months. I met her recently and she made 4 phone calls while I was sitting there, only stopped it when I said I was getting fed up and may as well just leave her to her phone calls. Last night she met me and another friend, and left about half an hour and said her parents were locked out. It felt like a made up excuse.
We have been friends about 4 years - prior to this we got on really well, but I feel very hurt and like she doesn't value my company any more. She said to me not long ago she feels envious of my relationship. Could this be the problem? She seems down but refuses to tell me what's wrong. I don't know what to do now.