Well done for coming through the op. I really wouldn't worry about the groin pain - you've got a long way to go with this recovery (6 months for a decent recovery and 12-18 months for total recovery). If you imagine all of the work that has been done, it's bound to be inflamed and sore. Have lots of rest, and keep using your crutches until it settles down. As for needing a hip replacement in the future - that would depend on how much cartilage damage there was in your hip (if any). This surgery is still realatively new in terms of long-term outcomes, but you could ask your surgeon at your next appointment.
Good luck with your recovery and let us know how you're getting on