What to do in Praha?

I'm going to Praha this easter with my boyfriend. We have never been there before, and I'd love to get any recommendations on what we should do. We're staying in the city center for three days. I'd love to get any tips on restaurants, attractions etc.I'm also wondering about how gay friendly Praha is. We never really show any affection for each other in public, but how would most people react if they knew we're boyfriends?