Dating outside marriage is not allowed due to various evidences from the Qur'ān and the Sunnah. From them is:
{Today [all] good foods have been made lawful, and the food of those who were given the Scripture is lawful for you and your food is lawful for them. And [lawful in marriage are] chaste women from among the believers and chaste women from among those who were given the Scripture before you, when you have given them their due compensation, desiring chastity, not unlawful sexual intercourse nor taking girlfriends. And whoever denies the faith - his work has become worthless, and he, in the Hereafter, will be among the losers.} [al-Mā'idah 5:5]
{And tell the believing women to lower their gaze and guard their private parts and not expose their adornment except that which [necessarily] appears thereof and to wrap [a portion of] their headcovers over their chests and not expose their adornment [i.e., beauty] except to their husbands, their fathers, their husbands' fathers, their sons, their husbands' sons, their brothers, their brothers' sons, their sisters' sons, their women, that which their right hands possess [i.e., slaves], or those male attendants having no physical desire, or children who are not yet aware of the private aspects of women. And let them not stamp their feet to make known what they conceal of their adornment. And turn to Allāh in repentance, all of you, O believers, that you might succeed.} [an-Nūr 24:3]
This āyah shows that you must lower your gaze and protect your private parts, which is not possible if you have a boyfriend. It is not possible to have a boyfriend without looking at him and it is near impossible to protect yourself from doing zina with him. Anybody who says otherwise is a liar or extremely foolish. Allāh said (meaning): {And do not come close to zina (unlawful sexual intercourse). Indeed, it is ever an immorality and is evil as a way.} [al-Isrā' 17:32] The āyah also commands the women to cover themselves up except in front of the listed people; the boyfriend is not one of them.
We have been commanded not to touch the opposite gender, apart from those who are you are allowed to (spouse, family etc.) The Prophet ﷺ said: “For one of you to be struck in the head with an iron needle is better for him than to touch a woman who is not permissible for him.” [at-Tabarānī; classed as sahīh (authentic) by al-Albānī]
We have also been commanded not to be alone with the opposite gender. Again, this is impossible to do if you have a boyfriend. The Shaytān will be with the both of you if you are alone and will entice you to do things you wouldn't think of ever doing. So if right now you think that "I can easily protect myself from zina if I'm with him", you will quickly find that things are not as you expect once you are alone with him.
The Prophet ﷺ said: “No man should be alone with a non-mahram woman unless a mahram is present.” [al-Bukhārī (4832), Muslim (2391)]
And he ﷺ said: “No man is alone with a woman but the Shaytān is the third one present.” [at-Tirmidhī (1091); classed as sahīh (authentic) by al-Albānī]
I hope that it is now clear that it is sinful to date outside marriage. As for what you said with regards to everybody in your school is doing it, then this does not change the fact that is is a sin nor does it make it acceptable. Know, may Allāh bless you, that the Prophet ﷺ told us: "Islām began as a something strange and it will return to being strange, so blessed are the strangers.” [Ṣaḥīḥ Muslim 145]
What does this mean? 'Abdullāh ibn 'Amr reported that the Messenger of Allah ﷺ said, “We are in such a time when the strangers are blessed.” It was said, “O Messenger of Allah, who are the strangers?” The Prophet said, “Righteous people among many evil people. Those who disobey them are more numerous than those who obey them.” [Musnad Aḥmad 6650, Sahīh (authentic) according to Ahmad Shakir]
And he also said “A time of patience will come to people in which adhering to one’s religion is like grasping a hot coal.” [at-Tirmidhī 2260 - Sahīh (authentic) according to Al-Albānī]
Therefore, you should not look at what people do and should instead focus on what Allāh commanded you with. It is sometimes hard but you must know in the end it is all worth it.