I keep saying it’s ok to relapse if it’s just the one to give myself a breath after the stressful day. I just need that one little bit to take the edge of that’s it. So I keep saying haha. It’s a problem and it’s always going to be a problem. But I hit the 21 hour mark and I’m just itching for relief. I can’t keep holding myself back, having a problem doesn’t become less of a problem just because you do less of it. I do hope that after this my withdrawals will be less intense. But it’s my birthday next week and then I start my first big girl out of uni job and I’m so stressed. But I need to believe in myself and see it as an act of service to myself because I deserve to have a happy life without the hold of addiction. Damn it! Why’s it gotta hurt so bad though!
I’m sorry you are going through this right now. 
You need to keep in mind that the thought process behind “just the one” isn’t based on rationality.
That is your addiction telling you it is okay.
However it’s never going to stay at just one.
It’s a downward spiral that can only be broken once these patterns are indentified and acknowledged as what they really are.
A disease.
The only way to stop this is breaking this cycle by whatever healthy means necessary.
This isn’t going to happen overnight.
It takes time and a lot of effort.
And that is also why it hurts so much.
Take the time you need and consider this your first priority, everything else is going to benefit from it. Including your mental health.
As for the question on how many times one can justify using? For as long as one is still breathing.
I wish you peace and the strength to get back on track 
It is hard. You really have to feel in your bones that one is never enough, this time won’t be different, and there is nothing worth relapsing over. Unfortunately, there is no magic way to feel this way. Going over your past, writing out how often you have fallen for the same minds tricks, how completely pointless relapsing is can help. Seeing it in black and white can make it hit home.
Your brain right now has a very strong pathway from any kind of intense experience directly to using your DrugOfChoice. It’s basically a high speed highway. Your neurons, all parts of your system are primed for this. It’s almost a reflex. No thinking required: Intense experience → use. That’s addiction.
This pathway has developed over time. You were not born with it. In fact you were born with very few such pathways. You had to learn them all: how to walk, how to chew food, how to pick up things. That’s how we humans work. We are born with only very few pathways and we aquire them by learning. By practicing them over and over again. The more often you activate a pathway, the more often you repeat an action, the stronger and faster a pathway gets in your brain.
After a while you are able to walk, speak, eat and do all kinds of wonderful things in your life without even thinking about it.
Unfortunately this also works for learning very unhealthy behaviours, like using drugs of all kinds. You aquire them by practicing. You strengthen them every time you engage in this behaviour.
Fortunately all our pathways can be weakened and even dismanteled. That’s called neuroplasticity. Your brain is capable of these changes through all your life. How do you do this? By not engaging in the destructive behaviour.
This is difficult. It requires a lot of conscious effort. It requires to go against all that you have been doing for a long time now. It takes time. It’s extremely uncomfortable. It’s like learning to walk.
So in order to dismantle this pathway in your brain you have only one way to do this: Do not use this pathway. Whenever you have any kind of intense experience, do something else. Do not use this pathway.
Every reason you find to use will strengthen this pathway. The reason does not matter.
What we do - our addictions - makes us sick, and it makes us tired. Are you sick and tired of being sick and tired?
You really gotta think about this, because we also kind of romanticize it: that warm feeling when we think about it; we kinda like it. When we’re in our addiction, we feel a longing for it, deep in the gut, in our body. It would feel good, we think. One time wouldn’t be so bad. I can start again tomorrow.
It’s a lie, of course. It’s always a lie. It always ends with regret.
Are you done with the lie? Because it takes resolve to make this work. You’re gonna romanticize it, especially in the early days. Are you done doing that? Are you willing to put in the work to see the results?
make it easy try a meeting plenty of resources out there to help wish you well