"Oh, what a tangled web we weave, when first we practice to deceive." So says Shakespeare. And a tangled web you've certainly been caught in!!!!
As far as I can see, your best course of action is to get a job (idling around in your sister in law's house is what got you into this mess in the first place; they say "the devil finds work for idle hands" and you certainly were the devils plaything weren't you!!!), and move away. You've managed to alienate your family by your stupidity, and the only way you can do something to give them any reason to forgive you is by standing on your own two feet and doing something worthwhile. At the moment you are wallowing in self pity and whining about your sister in law as if she's the love of your life, taken away from you. Get a grip, in reality, she's your brother's wife, not yours at all. What's going on in their marriage is not your business. I suggest you read what you wrote to us, and then think about the dishonesty you showed, never mind about anyone else's motives. You were driven by selfish lust, to the point where you are bribing servants, sneaking around, and making a fool of your own brother, you were a real viper in the nest!!! If your brother has changed his mind and forgiven his wife, that's their business; maybe he realises that children need a mother, whatever, it's nothing to do with you.
Now, stop with this self pitying BS and get out and earn a living and be a man, not a snivelling spoilt child.