I was told the green plant was a weed so i wanted to kill it so the red begonia could thrive. I cut off all the stems I found of the green plant and was wondering if it would actually die?

Doesn't look like a weed to me...
Kinda looks like a datura...

Personally, I'd probably dump out the pot and see if I couldn't separate the two... and repot the green plant into a separate pot.

God didn't create weeds... Ignore anyone that doesn't know what a plant is... and lazily refers to something as a weed.

Some plants may need thinning... some plants may have some bad habits, but until we know exactly what we have... not a weed.

Just pull it out of the soil and toss it.
No muss, no fuss.

Even if it's a Datura, Impatiens, fancy Hibiscus or Sow thistle, if you want a Begonia all by itself: it's a weed. A weed is a plant out of place, whatever it is. A rose in a cornfield is a weed.

I hate that belief!

Typical monoculture nonsense...

So easy to repot... A valuable plant is a valuable plant...

Could you please take a new pic of the other side of the plant? Then we could see what it is and discuss that actual plant, not the theory of what it might be and what might happen. If the ID could be decided, the other plant might be something you really like.

My suspicion is that the Begonia would be happiest with the additional plant because that's a lot of pot/soil for a rhizomatous Begonia. A bigger companion plant will prevent the soil from staying soggy too long. If you leave the seedlings, you'll probably need to guide them out of the way of the Begonia so they don't cover it and block the light.

Your begonia needs to grow without another plant in the pot! I would gentle in the removal if you want to see that the other plant becomes. If it is a Datura, they won't do well inside. My guess is it's not a Datura. Some plants return from their roots, so remove is the best thing.

Why would it "need" to grow without another plant? I have a bunch of Begonias with lots of other plants in the pots, and a lot of other people do too. There are a lot of pics of them in these discussions:
The thread "Group/companion/combo pots." in Houseplants forum
The thread "Show your Begonias" in Houseplants forum
The thread "This old grill" in Containers forum

Here's what it looks like now.

Sorry purpleinopps, I'm old fashion and enjoy the beauty of one plant in one pot and not crowd by others. If it was a Datura that is one plant that has many issues if grown inside with others. Dats are bug magnets!!

Nothing to be sorry about, your opinion is as valuable as any other. It just sounds like a personal preference more than an issue of the health of the plant.

I hope your Begonia does well, Breeezy! The new pic is too dark to see much but it should get a bit more light, or at least more even light, without the other plant(s) in the way.

If you want to identify a plant (or insect) you can get an app called Seek. You scan the plant with your phone and get the name. Then you can save it. It sometimes takes a bit of scanning from different angles.