Will I get fired for this?

All in all, it comes down to how much money the store has lost. If it is a lot... Like maybe more than 2.5k-5k dollars, you are in a lot of trouble. It also depends on how long you've been doing this. One day? Two days? A week? A month? But, I'm afraid there is a risk of you being dismissed.

If you were talking store inventory and selling it on Ebay and pocketing the profits from said sell, termination is the least of your worries , depending on the amount taken from the store felony theft maybe on the table

Additional Info, your additional comment changes things: So you legally purchased the clothing, probably at an employee discount, then choose to sell said clothing at a discount on Ebay , while not illegal it may have violated store policy by basically selling brand new items at a steep discount which it turns under cuts the stores profit

You're fired.

If you were buying using an employee discount and you sold more than one item there may be other problems you will be facing.

Very probably. You were selling company goods on eBay. Goods that didn't belong to YOU.

By any way of looking at it you were guilty of gross misconduct. That usually results in getting fired.

Did you purchase the items from the store before you sold them online? If not, did you turn in the money you got to the store?

If you did neither, you are guilty of theft and should be fired. You could also be prosecuted.

Yes you will likely be fired. You were either straight stealing clothes or using your discount to purchase and sell them.

None of that belonged to you, of course youll get fired.

You should consider yourself lucky if they don't report it to the police.