Others have already addressed parts of your question, so I'll tackle this part.
Slipping back into our old habits that are (spiritually) unhealthy is something we all do sooner or later, it's part of spiritual warfare. Satan attacks us where we are the most vulnerable constantly and yes, that means we slip and fall.
It's important to remember we're all sinners and no matter how hard we try, we will always sin in one way or another. What matters most is that we recognize it, seek forgiveness and try again. And again, and again, and again. As many times as we have to. Recognizing our sins and seeking forgiveness from them along with help from the Holy Spirit is key. That is what we are asked to do.
Now I'll tell you I certainly have my own problems not disappointing our Father in Heaven and as often as I pray and try not cursing someone through the windshield as I drive, I often fail. I count my victories where I find them and use that as encouragement to keep going. Don't just count the number of times you "slip and fall" into past behavior, you count the times you DO NOT. Acknowledge those victories, thank Jesus for them and keep going!!
Above all else, do not keep kicking yourself when you fall into a past behavior. Acknowledge it, pray about it and let it go. Try again. If you keep kicking yourself, Satan wins. Don't let him. That's not what our Father in Heaven wants from you. He wants you to keep trying and count the small victories where you find them. Give Him the glory for them and keep going.
Hang in there, it's a struggle and it's lifelong. It's worth it.
This says it best; without trying to 'justify' it's value with scripture.
As we've already seen in this thread; you WILL get 'helpful' instructions from all over the Christian spectrum.
MY advice (and it IS quite valuable! - smirk) is to read the NT and realize that each book was written to a different audience, keeping in mind that things written in one, to a specific group or individual, may not be applicable to all who read the text later.
Pray for understanding (it'll come) and allow that still, small voice (the Holy Spirit) to guide you.
Temptation comes to all of us; even those you might consider to be 'bible savvy'.
Sometimes the most 'bible savvy' can slip and fall; but ther are MULTITUDES of others who are around to help restore the fallen one again.
You are NOT in this alone; and you can see this by those just in this thread that have taken time to try to hep you on your journey!
Vaya con Dios!