According to the Oxford learner's dictionary, "see somebody" mean "to spend time with somebody". It does not say the 2 have a romantic relationship or not, so I reckon the 2 could be just friends or couples.
Say, Tom and Mary are just friends nothing more. They like to talk with each other, they they are never in love with each other.
Can we say "Tom has been seeing Mary for a while" in that situation?
Does the phrase "Tom has been seeing Mary for a while" always imply they have a romantic relationship?
To remove the confusion, do you think we just say "Tom has been hanging out with Mary for a while" or the likes?