I am 25, full time student and don't have a job. Can my boyfriend claim me in his tax return?

Maybe.  You would need to have lived in his home for the entire year and your gross income must be under $4,300 along with the other requirements under the Qualifying Relative rules.

To be a Qualifying Relative -

1. The person cannot be your qualifying child or the qualifying child of any other taxpayer. A child is not the qualifying child of any other taxpayer if the child's parent (or any other person for whom the child is defined as a qualifying child) is not required to file an income tax return or files an income tax return only to get a refund on income tax withheld.
2. The person either (a) must be related to you or (b) must live with you all year as a member of your household.
3. The person's gross income for the year must be less than $4,300 (social security does not count) in 2021
4. You must provide more than half of the person's total support for the year.
5. The person must be a U.S. citizen or a U.S., Canada, or Mexico resident for some part of the year.
6. The person must not file a joint return with their spouse.

Only if you lived with him the whole year and had less than 4,300 total income.

Here are the rules for claiming a dependent.  Do you qualify as a dependent?

https://ttlc.intuit.com/community/credits-and-deductions/help/who-can-i-claim-as-my-dependent/00/26781