Can I claim my girlfriend as a dependent?She lived with me all year.she goes to school part time and only worked 3months out of the whole year

How much was her 2017 income? Any scholarships or grants?

Around 3000 and she did get a grant

If she falls into this criteria, you can claim her.  Don't be tricked by the term relative, it can be an "unrelated" person also.

Under the qualifying relative rules:

• Not qualify as somebody else’s qualifying child or qualifying relative
• Live with you the entire year (365 days) or be one of these:
• Your child, stepchild, foster child, or a descendant of any of them
• Your brother, sister, half brother, half sister, stepbrother, or stepsister or a descendant of any of them
• Your father, mother, grandparent, or stepparent, but not a foster parent
• Your son-in-law, daughter-in-law, father-in-law, mother-in-law, brother-in-law, or sister-in-law
• Your uncle, aunt, nephew, or niece
• Earn less than $4,050
• Receive more than half of his or her support for the year from you

To claim a dependent, these must also be true:

• He or she can only have filed jointly with his or her spouse to claim a refund of the taxes withheld. Also, if he or she were to have filed separately from his or her spouse, neither would have owed taxes.
• The dependent is one of these:
• U.S. citizen
• U.S. resident alien
• U.S. national
• Resident of Canada or Mexico

You can’t qualify as a dependent on someone else’s return. This is true even if the other person doesn’t claim you on his or her return.

Yes she did live with me all year and I paid for all her costs, supplies etc.would I have to put her w2 form joined with mine or is it done separately?

No. You cannot include her income with yours since you are not married.  She will have to file her own return if she made more than $6350 from an employer or more than $400 from self employment income.  If she files she needs to mark that "someone else can claim me on their return."

and some of her Grant may be taxable.

"Earn less than $4,050" should say "income of less than 4050"