Losing best friend and no idea why

I've seen quite a few posts with similar problems to mine but I would love some advice!

I met my best friend at uni 5 years, and we instantly became friends even though we were in a big group. We became closer, lived together with other friends and even after uni finished we still remained close. We both said how much our friendship meant to each other and that we'd never had a friend like this before because we got on so well and genuinely loved each other. I honestly thought she would be a friend for life. We went through so much together- deaths, break up, mutual bad friendships, graduating uni and going on holiday together etc.

But, earlier this year she suddenly stopped talking to me altogether. I understand she started uni again and made new friends & found a new boyfriend which didn't bother me at all, but I literally didn't hear from her at all. (I have a feeling the new bf may be the problem, as soon as she started going out with him, I didn't hear from her at all).

I tried to carry on texting her first and arranging to meet up but then I realised if I didn't contact her, I wouldn't hear from her. I eventually told her how I was feeling and she started texting me a bit then I think she just gave up again.

Now, I honestly don't know what to do, I don't want to lose my best friend but it's horrible to have someone suddenly cut off for no reason.
(Also her excuse was that she's "too busy" to see me, but she's constantly posting pics of her out with her new group of friends and boyfriend).


SO, should I just give up? I don't know what more I can do since I already told her how hurt I am :/