Can't stop thinking about my daughter

I am grieving the loss of my 21 yr old daughter who stopped speaking to me 5 months ago for no valid reason. I don't feel like doing anything and don't know how to make life worthwhile at this point. Yesterday was her birthday and I'm crushed that she didn't respond to my sweet email. She doesn't respond to anything and acts as if I don't exist anymore after we had been so close. I noticed a change in her after she became seriously involved with her current boyfriend a year ago. He's very nice and I really like him, but it seems that she's discarded me now that she has him.