You should first of all think about taking a boyfriend is prohibited in Islam. Committing fornication is one of the grave sins which is promised evil consequences in this life and the hereafter, but Allah forgives all sins including adultery. He said in the Quran,

“Say, O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.” (Az-Zumar 39:53)

If you forgive him in this life, Allah will forgive him regarding your own rights but there are other rights which are left for Allah.

Almighty Allah knows best.