Hate to break out the 2X4 here, but WHACK! Ok, Shiny, this is HIS birthday so if he says no party...keep it simple, no party. I think asking him if he wants to go out and Karaoke is a great idea and if friends want to come along, great! And please don't read too much into him not wanting a party, either.
If he isn't working and things aren't 100% right now for the 2 of you, maybe he just isn't in the mood to deal with all the fuss. What does he really love to do? Could you plan something that involves just the two of you and some activity he really loves? No pressure for him, just something fun and easy?

I am responsible for my own happiness.