It's never easy being dumped! Only kidding of course but dogs are different. Some are more drawn to people. Some to other dogs. Herding dogs are usually very people oriented. Basenjis much less so. He may have decided you're not the perfect playmate -- too slow and a nag! LOL
He may also not be feeling great and/or be a bit pooped after all the excitement of the vacation. You may be experiencing the same thing. I say this because a 7 month Basenji would more likely be getting into trouble of some kind than sleeping all the time. Give it a bit and see what happens. My guess is that he'll return to something resembling the old normal. My advice would be to stop trying so hard and beating yourself up. FWIW you needn't worry about keeping your Basenji happy. He'll do that for you!
I also wouldn't worry too much about the play thing. I've had Basenjis who were wild for playing with other dogs until one day a switch turned off and they were over it. Sad but it's part of growing up.