It is your duty to repent...
How at all can He turn away a pardon seeker from His Court? God forbid. Such is not our opinion about You. He has made a must for both the parties at dispute to make peace. Whoever may make an advance; it is incumbent on the other one to respond positively. Reconciliation is a must for both the parties. One who goes first in this direction will enter Paradise earlier. One who made an advance did his duty. The other duty is to accept peace effort.
Anyone who said: I believe that God is Only One Allah and Muhammad is His last Prophet and I also give witness that Judgment Day is True and Accounting is True and that Paradise and Hell are True. Anyone who gave witness to these three basic facts and believed in them has also accepted all other essential orders of Islam, that is, all apparent things like prayer, fasts and Hajj, which no one can deny. He becomes a respectable Muslim. Shedding his blood is prohibited; may he belong to any sect.
Apparently he is a Muslim. His body is clean and his life and honor are safe and so also his possessions and marriage with him is also valid. We have nothing to do with his Hereafter. Hereafter is relevant with a special meaning, but all the apparent orders (worldly matters) are based on the above mentioned three basic beliefs, be he a Sunni or a Shia. Sunni and Shia, both are Muslims.