Bernie is crying because some guy is threatening to attack him. Niko says he'll help, so he's going to use Bernie as bait to find and take out the attacker.
To Middle Park
Grab a vehicle and take Bernie to Middle Park. After he does his stretches, he'll go for a jog. You need to follow him, but not too closely. Give him about a 3 second head start, then try to stay that distance behind him.
After he runs through the tunnel, he'll be attacked by the homophobic guy. Chase after him and fire off a few shots, then jump on one of the scooters near by. Chase him all the way around the park and museum grounds and drive-by him when you get close enough. Once he's dead, you may get a wanted level. You'll be told you collect Bernie, but I'd suggest trying to lose the stars first.
Head over and grab Bernie and take him back to the place he wants to go. Why not grab a taxi to make it a little bit quicker?
- If you pick up Bernie on a motorbike vehicle, he'll pull on a nice shiny pink helmet...
- Always lose the cops before you pick up Bernie. You won't fail the mission for leaving him behind.