For transgender people, coming out to a cisgender boyfriend or girlfriend surely isn't an easy thing to do, while cisgenderism is extremely common.
As far as cisgender people go... In some cases, they don't care whether their partner is cisgender or transgender, and the fact that their transgender partner is transgender doesn't change their feelings for that person (this is an example of unconditional love). In some other cases, it takes them time to accept that their transgender partner is transgender. And in different cases, they aren't comfortable being with a transgender person.
It's so good that all is well in the end between this guy and his transgender girlfriend, thanks to that kind elderly man.