physical constants are useless in game developement. you just need the formula F = G * m1 * m2 / Distance^2 and you have to play with G in order to get the results you want.
so you have two bodies with masses m1,m2, velocity vx1,vx2,vy1,vy2, position x1,x2,y1,y2 then in the main loop to simulate the gravity between them you do:
distance=sqr((x1-x2)*(x1-x2)+(y1-y2)+(y1-y2))
F= G * m1 * m2 / (Distance*distance)
xcomponent=(x1-x2)/distance
ycomponent=(y1-y2)/distance
deltav1=F/m1
deltav2=F/m2
then
vx2=vx2+deltav2*xcomponent
vx1=vx1-deltav1*xcomponent
vy2=vy2+deltav2*ycomponent
vy1=vy1-deltav1*ycomponent
and the usual
x1=x1+vx1
x2=x2+vx2
y1=y1+vy1
y2=y2+vy2
that's all
so you have two bodies with masses m1,m2, velocity vx1,vx2,vy1,vy2, position x1,x2,y1,y2 then in the main loop to simulate the gravity between them you do:
distance=sqr((x1-x2)*(x1-x2)+(y1-y2)+(y1-y2))
F= G * m1 * m2 / (Distance*distance)
xcomponent=(x1-x2)/distance
ycomponent=(y1-y2)/distance
deltav1=F/m1
deltav2=F/m2
then
vx2=vx2+deltav2*xcomponent
vx1=vx1-deltav1*xcomponent
vy2=vy2+deltav2*ycomponent
vy1=vy1-deltav1*ycomponent
and the usual
x1=x1+vx1
x2=x2+vx2
y1=y1+vy1
y2=y2+vy2
that's all