All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
You are not obligated to perform ablution unless semen is ejaculated with pleasure. From your question, it seems that what came out was not semen but rather pre-ejaculatory fluid, so you are not obligated to perform ablution. Instead, you should perform Istinjaa' (cleansing) for it as you would for urine.
And it is incumbent upon you, dear brother, to repent to Allah from watching prohibited things and masturbating. You are in the prime of youth, so do not fill your pages with sins and disobedience; fill them with acts of obedience. The youth stage is one of the most crucial phases in life, and a person will be questioned about it, as mentioned in the hadith: 'The feet of the son of Adam will not move on the Day of Judgment until he is asked about five things: his life and how he spent it, his youth and how he used it, his wealth and where he earned it and how he spent it, and what he did with his knowledge.' [At-Tirmidhi]
If you are able to get married, then hasten to do so. In a hadith, it is mentioned: 'O young people! Whoever among you is able to marry, should marry, for it restrains the eyes and protects the private parts. Whoever is unable to marry, he should fast, as fasting diminishes his sexual power.' [Agreed upon by Al-Bukhari and Muslim].
Allah knows best.