It's hard to explain in words
well thats the beauty... you dont need to. I (as others I assume) know exactly what you mean. No need to break your head trying to express it. I get it.
It is hard to lose a loved one, whether human or animal... but in the end we move on and those memories and feeling brought on by said loved ones is what makes us who we are... they add to us something that we would never of had if it wasnt for them. So even though "they" always seem to leave us... "they" also bring something invaluable to us...
love! without it we just arent complete.
IMHO ... although we lose and have lost many loved ones in our life times... I wouldnt have it any other way... I cherish those memories and feelings more than all the money in the world. All my family members and animal companions that I have lost will live with me 'till the day its my turn to leave this world.