If it's been more than 15 days, and the issue is not bothering you and your best friend. Then let it go. And it is bothering you, you should sort the things out.
If you think it was your mistake talk to your friend and accept your mistake but if it's his/her mistake then you should wait for sometime and if still nothing changes then move on coz in this life no one care better than your family
You must talk it out and clear as to why this happened or you can talk to someone else you trust let it out, share and ask for a good suggestion and advice. Ask your friend if something happened unintentionally and take measures to amend it . It will be fine
If it is not bothering him then you should move on. It’s better to have a good friend who is with you during thick and thin rather than one who is just with you for hanging out.
Did anything happened between you two? Maybe your friend is busy. Or your friendship has run it's course, then you need to move on with life. Find new friends, interest etc. Life is too short to worry about one person.