This sounds like a reverse PUA problem...
If I didnt know any better I would say he is doing push-pull. Or playing hard to get.
I think Stormy is right though.
It might be that you have gone into his JUST friends cathegory, guys do it to each other all the time. Like inviting people to come along but if the other person doesnt come then we wont force him.
As guys we learn to deal with these situations since we get exposed to it so often. We are always (almost always) invited this way. So when someone actually cares enough to make an effort to be with US, we are so grateful! If it is a guy we make him our new best friend because he has flattered us. If it is a girl we fall in love...

No but it does happen.
We are not used to get a very special SPAM and you are experiencing a guy thing from a girls point of view. It is quite interesting, you have actually taught us something by telling us this! I will use this to my advantage.
Ezo
BTW good luck!