I'm 17, can or will I go to jail if I have sex with my girlfriend(13)?
If I do go to jail, how long will I be in for?
Even if both of us want it, and we love each other?

At 17 years of age, you would likely see a family court judge first. The family court judge would evaluate the case and make a determination as to whether to send it to adult court. In most states, 17 year olds are tried as adults in felony cases.

Under Title XLVI Chapter 800 Lewd or Lascivious offenses committed upon or in the presence of persons less than 16 years of age.

800.04 Lewdness; Indecent Exposure

LEWD OR LASCIVIOUS BATTERY. A person who:

(a) Engages in sexual activity with a person 12 years of age or older but less than 16 years of age; or

(b) Encourages, forces, or entices any person less than 16 years of age to engage in sadomasochistic abuse, sexual bestiality, prostitution, or any other act involving sexual activity

commits a felony of the second degree, punishable as provided in s. 775.082, s. 775.083

LEWD OR LASCIVIOUS MOLESTATION.

(a) A person who intentionally touches in a lewd or lascivious manner the breasts, genitals, genital area, or buttocks, or the clothing covering them, of a person less than 16 years of age, or forces or entices a person under 16 years of age to so touch the perpetrator, commits lewd or lascivious molestation.

An offender 18 years of age or older who commits lewd or lascivious molestation against a victim 12 years of age or older but less than 16 years of age

commits a felony of the second degree, punishable as provided in s. 775.082, s. 775.083

IGNORANCE OR BELIEF OF VICTIM'S AGE.--The perpetrator's ignorance of the victim's age, the victim's misrepresentation of his or her age, or the perpetrator's bona fide belief of the victim's age cannot be raised as a defense in a prosecution under this section.

PROHIBITED DEFENSES.--Neither the victim's lack of chastity nor the victim's consent is a defense to the crimes proscribed by this section.

775.082 PENALTIES: For a felony of the second degree, by a term of imprisonment not exceeding 15 years.