My little one has nipple confusion. HELP!

This past Monday and Tuesday, I left our three-month old baby with his great-grandmother (who is visiting us from the Philippines) because I had errands I really needed to do. I was gone all day, which means Nathaniel had to eat expressed breastmilk through a bottle. This is the first time I have been away from my son for this long amount of time and who knew that in only two days, he will develop nipple confusion. Breastfeeding has been a battle, he is not properly latching, and he exhaust himself from crying so much that he ends up just falling asleep after the letdown reflex has slow down. However, any feeding after bedtime is still the same and I think it's because he is too sleepy to notice the difference.

I have tried feeding him in a dark room where stimulation is at minimum, feeding him when he's happy or as soon as he wakes up, and pumping to keep my supply up.  I'm not worried that he's not eating enough because he still has plenty of wet diapers a day. I'm just wondering when will he be "unconfused"? And will it always be like this every time I leave and when/if I go back to work?

I feel like I'm back to the newborn days when it comes to breastfeeding, which is something I'm just not ready to go through again. And this time, I don't think I'm strong enough either or even has the will to keep persevering... Oh, how quickly that feeling of inadequacy just creeps back in :(