of course, but both of them must love each other more than any thing at the world

I don't think the word "forever" is applicable to our world at all. Everything has its beginning and its end. "This too shall pass" "Sic transit gloria mundi" etc. B-) Though if one prefers to believes in it.. it's their right to choose which reality to believe in.

Agape love and parental love are everlasting.

No

It depends on understanding and situations