Opinions?

There is no right or wrong to this. It's whatever works for you both.  What your sister does is immaterial.

But if you earn very different levels of income, a fair way to split costs is for you both to pay a percentage of your income into a joint account. That joint money then covers rent and bills.

Roommates pay half, INCLUDING RENT.

Partners pay whatever they agree to.

At $225/week, you are the same as $12000 a year, or 40% of combined gross.  You could ask to pay for 1/2 the food, 1/2 the utilities and 40% of the rest.

It's whatever you agree on.  But my opinion is like your dad's  - it isn't fair.

Wrong?  If two people share a space and expenses, it makes sense that each would pay 50% of the rent and other expenses if they are not legally married.  What's "wrong" about that? Your income doesn't change the fact that you use 50% of the space, food, electricity, hot water, etc. 

None of this is your father's business.  You and your "partner" are the only people who need to agree on how to split your expenses.  If you want to pay a less of your salary towards rent, then you and you partner need to find a cheaper place to live or. your partner needs to agree to pay more than %50 of the rent.  If you don't want to pay any rent, why would you expect someone else, even a lover, to cover your expenses?

If you are ok with the arrangement,  it's fine. 

This is entirely between you an your partner, it is no one else's business how you split the bills.  

Many people consider a fair split to be proportional to income. If you earn $11K and he earns $18K, and the rent is $500, then you should split the payment $190 to $310.

Here's why: you didn't choose this apartment based on your ability to afford it. You aren't his roommate. The two of you decided to live together and chose an apartment based on your combined income.

That said, it sounds difficult to actually compare the two incomes. You're in "training" and will presumably get more hours and earn more after you finish. He earns commissions on an erratic schedule and is probably earning a lot less in 2020.

Each family or couple decides how to pay the bills and deals with their finances. Parents, family, friends, strangers can give advice but only the couple can decide. There is no right way to do this. There are wrong ways, abuse, making someone feel crap for every cent spent, gaslighting, hiding credit card debt, but there is no magic formula of fairness.

 You use the house, eat the food, use water, use electricity, internet. so half the bills are arguably yours.

You and your boyfriend came to an agreement about things when moving in together. You can try to change things but that might mean someone is hurt, there is a break up or someone has to move. If you are happy, and have some disposable income to save or treat yourself then be happy. Tell you dad to stay out of it.

If you are unhappy about the arraignment then make a change, with your boyfriend or by yourself in your own place.