I've actually torn my hip flexor before, and once it's damaged, it never fully heals simply because it's almost always being used.
Depending on the pain and no pain, ice and excessive stretching will help, that is when it's sort of already healed.
I've asked my doctor buddy, and he says there are many little muscles in that one area that make up the hip flexor, and any "1" of them or more, can be damaged.
You can self-diagnose, and do your own self-recuperation regiment, or go see a pro,and let him take a picture to specify, but you'll still do the same overall regiment. I already mentioned it.