You know how the farther two objects are away from eachother, the less influence these two objects exert over eachother.....??
For example the good ol` distance squared rule....
Any two objects of any two masses, will exert a force proportional to the product of their two masses and inversly proportional to their distance squared. Basicaly, the gravitational force felt between any two objects placed a foot apart, will be a fourth as strong if the two objects are placed two feet apart. It will be a ninth as strong if they are three feet apart, a sixteenth as strong if they are four feet apart and so on. Well this same rule applies to the electromagnetic force of nature, where the product would be the two charges.
All this mumbling on about forces and distances was only to make this point: if you placed two electrons a foot apart, the gravitational force felt between them is the same as the electromagnetic force felt between them if they were placed a light year apart. (Don`t quote me exactly because the units may have been in meters not feet). But the point is the force of gravity is by far weaker than the electromagnetic force, and even more-so than the strong nuclear force. Of the four forces of nature known to science, gravity is the all time most feeble force. That is where you got "weak" and "gravity" together.
Notice I never mentioned the term
"quantum"......thats because gravity being weak has nothing to do with whether or not it is felt on the quantum level. Don`t get this confused with what is actualy a force "the weak force" which is a force that plays a role in particle phyisics and quantum phenomena (it is the weakest of the so-called quantum forces). Is this where you got the distinction of weak and strong mixed up with graivity and the quantum level...??