I'd go with a golf theme party since that's something he does for fun. Found several different sites that might help you with a golf themed party:

1) www.party411.com; (had ideas for decorations, etc.);
2) www.partywedding.com; (under party accessories-tableware they had napkins, plates, cups & table cover with golfer on it);
3) www.gulfun.net; (had section with golf jokes & quotes, gag gifts, etc.)
4) www.personalizedgolfballs.com;
5) www.golfgiftsetc.com;

Hope this helps.

Been thinking about the golf themed birthday party, here's somethings I remember from looking at some of the sites and some others I came up with:

1) Cover the table with a green paper or plastic cover (for
that grass effect);
2) Find a picture of the boyfriend playing golf, find some
old golf magazines, etc. and cut out pictures of famous
players. Go to a photocopy store, cut, paste & photocopy
the picture(s) of the boyfriend & famous players so it
appears he had been playing golf with them. You could
do individual pictures or make one large poster board
with several of them on it;
3) Fill a jar with golf tees and have the guests guess how
many are in the jar and give a prize for the closest
guess;
4) Make flags like they use in the holes (large or small)
maybe made with tooth picks to be used in the food;
5) Find some of those candle holders you find at craft
stores where you can put a candle in the center of the
holder and then fill the outer rim with golf balls or
golf tees;
6) Saw a miniture golf bag cooler on one of the sites I
mentioned, could use that as a centerpiece. Fill it
part of the way with tissue paper then use some of that
green Easter grass and place some golf balls on top of
that and around the bottom of the bag;
7) Could have your local grocery store or bakery make a
golf themed cake;
8) Get a couple of those topiary forms from the craft store,
maybe one that already is set up in a pot, then hot glue
golf balls on the top, fill the pot with that Easter
grass, tie a couple of green and white ribbons on it.

Hope some of these ideas help. What ever you deceide on hope you have fun and your party is a success!!