Does the repentance of one who has committed adultery for many years and is addicted to pornography, while feeling that Allah detests him and wishing to commit suicide, with the knowledge that he will marry the woman with whom he committed adultery, get accepted?

The mercy of Allah Almighty encompasses all things, and no matter how great the sin, the forgiveness of Allah is greater. So, do not despair of His mercy. Cut off your relationship with the girl and repent to Allah with sincere repentance. Your marriage is not permissible until after repentance. Take the means to be steadfast, such as keeping the company of righteous people, adhering to dhikr (remembrance of Allah) and dua (supplication), preserving the obligatory prayers, frequenting mosques, increasing fasting, and contemplating the Day of Judgment. Have a good opinion of your Lord, for one who repents from a sin is like one who has no sin. Beware of satanic thoughts and despair of Allah's mercy, for only the misguided despair of it. Turn over the page of the past and start a new page with Allah through repentance, turning to Him, and doing what pleases Him. If the time for marriage comes and the girl has repented, then marry her; otherwise, look for someone else.