Sometimes relationships are a little like when you were a kid and chased butterflies.
You wanted that particular butterfly, that gorgeous beautiful butterfly and you would chase it, over stock and stone.
And then when you catch it, triumph wells through your body and you proudly puts it in a glas-jar and shows everybody around you how beautiful butterfly you caught.
Then the butterfly dies.
You're sad a little bit, but then you forget about it and set out to catch another butterfly.
One person in the relationship is afraid the other one will leave so holding the other person harder and harder, as not to loose them.
If you hold the butterfly too hard you will crush it, kill it. Then you don't have a beautiful butterfly anymore, you have a crushed butterfly.
There is no way you can hold a butterfly without killing it eventually.
Some butterflies flutter into your life, make your day seem a little more brighter, then flutter out of your life. Enjoy them as much as you can. If you try to catch it you will either succed and kill it eventually, or you will be disappointed because it escaped.
Some butterflies come to stay and them you can enjoy as much as you want, but do not try to catch them, because an imprisoned butterfly will do nothing more than try to escape and so looses their elegance, their beauty, and when they get free (or die) they will never come back.
Let the butterflies flutter free through your life, enjoy those who stay and wish those who go godspeed.