Why did my ex boyfriend say he wants to be best friends but completely ignores me?

My boyfriend broke up with me a couple or more months ago, when we were going out he said he would always want me in his life if we broke up. When we broke up there was nothing I could do so I agreed and said I would like to be friends, he said being best friends would be perfect seeing as our relationship didn’t work. So far, he has not contacted me at all, he also has my best friends guitar and we asked him to bring it back, he said he would the next day but never did and avoided her calls. I sent him a text saying ‘please bring it back because it belongs to her and it would be good if you could bring it back in the next couple of days’ (i didn’t want to contact him because i was happy leaving him be) he said ok, no problem but never did… what should i do? what does this mean?