Man, imagine being a loving father of many cute, adorable fillies that your marem fucked out of you, that you could care for and love for eternity, playing with them, cooking for them, sleeping with them, cuddling and kissing them, hearing them say "I love you, Daddy" as they hug you in return for your love and care.
That even when they grew up into becoming beautiful and feminine mares, they're still adorable and innocent fillies in your mind as if they're still the same little fluff balls as if they were pre-puberty.