Consider whether there is a new relationship in your friend’s life. Sometimes a new boyfriend/girlfriend or a change in family members can cause a person to change their friendship priorities. It’s not an excuse to go silent but it may be a reason behind the silence.
Put this down to experience. Sometimes people do things in life that you just can’t fathom but it’s down to their internal issues, not about who you are as a problem. Ultimately, it’s their loss as much as it is yours.
Consider whether you might have said something unkind, hurtful or thoughtless that encouraged your friend to feel a need to distance themselves from you. Listen to your gut. In some cases, it’s not one thing but a series of little things that lead to a “last straw”, when someone has finally had enough of excuses, bad attitude or broken promises. Is that possibly the case? Have you been a bit of a self-absorbed nuisance lately? In some cases, if you’ve been going through an “it’s-all-about-me” phase, such as planning a wedding or going through something major in your life, your friend may have reached the endpoint of coping with your drama or neediness.
Tell your friend that you’re happy to resume being friends whenever it feels like the right time for them. No pressure, no judgment. More help can be found in How to confront someone who is giving you the silent treatment.