The deal is closed and I'm ***ed up xD

Well orgasm and ejaculation are different processes that can happen independently. Since both females and males can have orgasms then I would think cum would be the synonym for that making nut mean ejaculation. Though some females can also ejaculate after a fashion male ejaculate is more common and is associated with the testicles and I think that reinforces my interpretation.

You either bust a nut or cum all over, you're using those words the same way

I’ve always used them interchangeably. I’m merely trying to interpret the difference implied in this particular meme.

I know it's not what you meant but now you have me thinking about cumming without anything coming out and now I'm very uncomfortable

Guys train themselves to do it. Ejaculation, not orgasm, is what causes the refractory (cool down) period during which you lose your erection for a while. Once you learn to consciously separate the two you can have multiple orgasms and stay hard the whole time.

I'm referring more to essentially being backed up with jizz

I’m sure there is increased buildup but I’ve never read anything about it being uncomfortable. Of course if it was you could just finish up. We all know how relieving it is to pee after your bladder is super full so it might be another enhancement to the experience.