How can I fix or prevent getting holes in my jeans near the crotch?
It's likely caused by the friction of your inner thighs rubbing together causing the material to wear in that spot quicker (especially because there are a few seams right there).

This can also be exacerbated by wearing pants that are too tight so that it's relatively tight around the upper leg or ones you shrunk by washing in hot water and running them in a dryer. If you're going to dry them you should wash them in cold water and dry them on low to minimize shrinkage. I have shrunk great jeans before and had to get rid of them because I made them too small. Finding a different pant cut may alleviate this, however, this will probably happen to any jean if you wear and wash them too much so if you can have more pairs of jeans and wash them a bit less they'll probably last a little longer, but it's pretty much always going to happen eventually.

You could fix them by sewing a jean patch on (cut up a different pair of jeans or buy a patch from the store) but you have to remember you're going to add more seams and a patch of jean that's either a different color or older/newer jean material and it probably is not going to last all that long.