When two souls that are twins come into a Union I have noticed that both their consciousness merges.You grow at a similar rate, and experience the same thoughts, and new depths of understanding as ONE.
It's not easily explained, it has to be felt. I have found times where one will change an aspect about themself at their own will, and you'll wonder... The key to this is not to mention anything, and you'll see both of you will become more like eachother everyday.
Basically, they will give you what you lack within yourself, and you will give them what they lack within theirself, fragment, by fragment, in a very slow process sometimes painful, but eventually that is what makes "one" whole.
That is the formation of twin-s-elves.
I've found to speed up this formation is forgivness. Forgive them if they hurt you unjustly, forgive them for what horrible things they say, forgive them for being nasty. Forgive yourself for reacting. Unconditionl love is partner to unconditional forgivness, combine both, and it will work wonders with a relationship. That is not saying be a doormat, say what you beLIeVE, but forgive them.
Forgivness can eliminate any karma you receive from the other. Everything balances out.
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"And dreams, don't ever forget, are the first step in manifesting wishes into reality"-- Linda Goodman's Star Signs