When I go out with my girl-friends, I always pay for them, but they do have their own money,?

Everytime I'm out with my female friends, I always pay for them, be it train fare or dinner bill, I pay. BUT, they do have their own money and own jobs, and when we go out, and it's time to pay for the bill, it's just a bit awkward, because I don't know if they are going to pay for the whole thing or just their share, so I just quicken the time up and pay the whole myself. I work, for St John Ambulance, I'm a Volunteer First Aider. So I don't get paid. I think I'm selfish if I don't pay for them. Is it true. What should I do when it's time to pay, pay my share and be done?