Ok, in this case the bitcoins return to my wallet?

I did a transaction from 1NxmG7uszkcUKgNEbvjrxmvajepMgdVg8S to 1BgfipEQDEbKktqxC1cCSP6g2Ke3oAVFhh, the tx is c48b65bceb6dcaf02816b09e70f74f2dfdb6bf28e1ba48db9392f02ea097edce, but this transaction disappeared, I can't find it anymore. Can anyone help me to know what happened?

So the bitcoins returned to 1NxmG7uszkcUKgNEbvjrxmvajepMgdVg8S?

How the owner of 1NxmG7uszkcUKgNEbvjrxmvajepMgdVg8S can avoid this situation in the future?

And this other transaction https://blockchain.info/tx/3538fa649cecf188fbfd4afc5722b019f57ed9fa28138c3f1ea180f4ac8fcf32 is to other address, with other value an in other date, why this invalidate the first transaction?

Sorry for these questions, I'm newbie in bitcoin.

Hi, I did a transfer for an addres on 23/11, an today I see that transaction disappeared. I saw here there is no transactions to the address

https://blockchain.info/address/36Bnc7Gg7mgJxnCjwiAmvnFX3BphEdVFs1

So in that page I clicked in on 'Unspent Outputs', and my transaction appeared in this page with the tags 'Unspendable!' and 'Unconfirmed Transaction!', look:

https://blockchain.info/unspent?active=36Bnc7Gg7mgJxnCjwiAmvnFX3BphEdVFs1&format=html

And when I click on the tx, my transaction appears in a page with the tag 'Double Spebd!', look:

https://blockchain.info/tx/cb6f76c402e55af7f63fe038ac52ebe468cf7d4f4c87ef0251268ab8fe45de02/1[/url]

[url]I did not understand, can anyone help me to understand what happened?