Should my friend change his religion so he can date this girl he likes?

Some although a small portion of the Orthodox have received the Holy Spirit.For this reason the girlfriend might continue to reject your friend,assuming he is a born-again Christian, even if he converts to her faith because most Orthodox Christians do not believe in the work of the Holy Spirit.:be polite:

When you love someone it is not about religion. It is a personal relationship. If it don't work out then you converted for nothing.

Oh yes, this has worked out well each and every time it has been done with no failures whatsoever.