Saying thank you is always good. I would do it with a fairly plain "Thank you" card and keep it neutral. "Thanks for your kindness in buying the ______ for me. I appreciate your thoughtfulness. All the best, Rebecca." No hints or innuendos or anything. Very flat and polite.

Couples often choose to spend most of their time together as a twosome and to avoid things that threaten the "couplehood" - you are not exactly a former girlfriend of his, but you have the same effect in light of past expressions of feelings for him. It's not the same as it was before. You don't need to attach blame, you just need to accept that.

I would be cautious about further approaches from him - unless you are prepared to lose your best friend in favor of an emotionally confused man.