You're in no way a failure.
Breastfeeding isn't easy. It's a damn hard skill to learn. For three weeks, every feed I thought to myself, "If I'm still doing this tomorrow, it will be an outstanding thing". It was horrific. Then all of a sudden, that 'tomorrow' came & it didn't hurt. It was weird - the pain didn't taper away, it just vanished. I have no explaination for it at all.

Like MissyMoo says: you CAN go back if you want. It's definitely not easy, but you can! express a little each day (multiple times if you can) & you'll keep your BBs working. When the mastitis has gone & your nipples have healed, you can give it another crack (hopefullly not in the nipple, eh?).

Now cuddle that bundle of yours & know that everyday, you are doing the very best you can. That's all your baby will ever ask (and they're pretty forgiving too. )