If I live on student loans, does someone else need to claim me? I understand that loans/grants/scholarships do not count as income. So then how do I file?

The question asked is "Can someone else claim you as a dependent?"

Since you don't live with your parents more than half the year, the "qualifying child" dependent category is a No.  That leaves "qualifying relative."  A person can claim you as a qualifying relative dependent if they provide more than half your financial support.  If the person is not a blood relative, you also have to live with them the entire year.

For support, you need to determine your total financial needs for 2020, that includes rent, food, utilities, transportation, medical care, tuition, entertainment, and clothing.  If you live in your boyfriend's home rent free, then your need includes half the housing expenses (food, rent, utilities).

Then, determine how much you provided for yourself.  Support you provide yourself includes money you earn or spend from your savings for your support, and it includes student loans in your name.  Scholarships are not counted as either support or need, they are not added on either side of the equation. 

Support provided by your boyfriend includes half the value of your housing (rent, food, utilities, etc.) plus any other costs he pays for you, like clothing or transportation.  Your parents might provide some support if they cover you on their medical insurance.

If your boyfriend pays more that half the overall total, then he can claim you, otherwise he can't.  There is a worksheet here that may help.

https://www.irs.gov/pub/irs-pdf/p501.pdf

Your parents can not claim you because you do not live with them and they do not support you.

Can your boyfriend claim you? There are two types of dependents, "Qualifying Children"(QC) and standard ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, student status, a relationship test and residence test. 

A person can still be a Qualifying relative dependent, if not a Qualifying Child, if he meets the 6 tests for claiming a dependent:

1. Closely Related OR live with the taxpayer ALL year
2. His/her gross taxable income for the year must be less than $4300 (2020).
3. The taxpayer must have provided more than 1/2 his support

In either case:

4. He must be a US citizen or resident of the US, Canada or Mexico
5. He must not file a joint return with his spouse or be claiming a dependent of his own
6. He must not be the qualifying child of another taxpayer

Loans are not income for the income test (#2). They are support not provided by your BF for the support test (#3).  Scholarships and grants that are used for qualified educational  expenses (QEE)(tuition, fees, books and course materials) are also not income, but they are support not provided by the BF.  

The IRS has a worksheet that can be used to help with the support calculation. See: http://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf The support value of a home is the fair market rental value, divided by the number of occupants.

Unless you determine that some of your grants are taxable (and you have more than $12,400 income), you have no income to file a tax return for. 

If you are over 23, there may be a refundable (up to $1000) tuition credit that you can claim by filing a tax return. This is not available if you are your BF's dependent. 

He doesn't claim you just because he pays the rent. You would have to meet the qualifications of a Qualifying Relative. You are not required to support yourself with taxable income.

Qualifying Relative

You can claim a child, relative, friend, fiancé (etc.) as a dependent on your 2020 taxes as long as they meet all of the following requirements :

• You provided more than half of their financial support. More info
• They made less than $4,300 in gross income during 2020 unless they are a qualifying child.
• They live with you or they are related to you. (Your relative must live at your residence all year or be on the list of “relatives who do not live with you” in Publication 501.) 
• They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren't (or won't be) claimed as a dependent by someone else.
• They aren’t filing a joint return with their spouse.
• You are not being claimed as a dependent on someone else's return.