I have never dyed my hair, but I regularly relax it. I strongly recommend that you look for protein treatments for your hair and that you start deep conditioning it often. Aloe vera gel makes an excellent moisturizing treatment (just put it in before you shampoo your hair). You can also put jojoba oil, sweet almond oil, coconut oil, shea butter, and etc in your hair.
Since bleach does strip away the protective layers of your hair, I think that it might really benefit you if you could consider shampooing less often. Shampoo is wonderful, but it can really leave your hair stripped if you use one that is too strong for your hairs' needs. Or you can mostly shampoo your scalp because if you shampoo your actual hair strands with a cleanser that is too strong then your hair strands will become even drier.
If you can, I second the idea of you starting to cut the damage off. But if you just can't let go of the length, then know that you will have to seriously baby your hair. That means that I would seriously recommend that you avoid blow dryers, flat irons, curling irons, pulling your hair too tight, and brushing your hair while it is wet (wet hair is extremely fragile).