well you can be as grey as you want. It depends how upfront you are with them at the start.
For instance I have a translator FB atm. At the start I was honest "Look I think you are really attractive and fancy the pants off you
but I dont think we get on well enough to have a relationship but I'd still like to see you as more than a friend".
Personally I tend not to mention seeing other people but assume that they are too. I also try not to see them more than once/twice a week so it doesnt get too serious and you can divide your time up equally.
It wont work every time as some girls want more but if you have an abundance attitude and always approach you should always be able to have at least 1 girl you are seeing.
Phil would probably be the best bloke to answer this...