I'm not sure if I'll be much help, but this makes me think of a similar situation with me and a female friend (who I used to like but we're just friends now). She lives a long way from me but we'd been talking all the time via text/whatsapp (at least 2 hours a day) for a while. Anyway, at one point she completely stopped replying to all my messages and when she did reply she gave very short answers and didn't seem talkative at all (this continued for a few days) so I asked her if she was alright and said that she didn't seem quite her usual self, but she replied to say that she'd been busy (although I honestly doubt she'd been so busy that she couldn't even reply to a text message, especially since she seemed to be on whatsapp almost constantly).
Anyway, a few days ago I was at a uni open day that I knew she was going to, so I called her and said that if she was about and wanted to meet up she should text me. Towards the end of the day, she called me and said that she was leaving, and I didn't have time to say hello to her or anything. I texted her afterwards to ask what she though of the uni and she didn't reply. She was at another open day yesterday (as was I) and I texted her to ask her if she was about and wanted to meet up, and she's ignored that as well. Sorry to hijack your thread, but if anyone has any advice as to what I should do that would be appreciated.