As an aspiring pua, its hard to not blame myself for when my relationships go wrong. After a two year LTR she breaks up with me and is with someone else a week later.
How to deal with the guilt of things going wrong and her losing attraction? because after entering the pua world i feel like whenever something goes wrong it was a flaw on my part, and that makes it much harder to get over it.

You only feel that way because you have a much better understanding of social interactions. Try to learn to forgive yourself even if it's hard.
There's no telling if it was you to blame, after all most 'real' relationships end after about 2 years because people aren't in love anymore. Get yourself a new girl and you'll be cure in no time!

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Optimistic?

Don't fuss about it man. The downfall of a true PUA is thinking "Hey if I act like this ANY and EVERY girl will want to be on the end of my cock till the end of time" this is a nice imaginary prospect but doesn't work in reality.

People grow up including girls. Anyone will tell you that PUA tactics won't work on some girls because they are fully prepared and ready for the lives they have with their boyfriends/husbands and are enjoying the fuck out of it.

Apart from that...never blame yourself because just note the things you did wrong and improve upon them. This kind of thinking is HARDWIRED into girls heads (this is why girls always think their right...because hardwired they think their wrong so thus they want to argue to make themselves right...thus why girls are so bitchy by nature.) Think about it when you meet a girl that knows shes wrong she will never admit it because she doesn't want to be wrong because wrong = beta.

But yeah my main point is that when you and your "missus" are happy in a relationship then PUA tactics won'r work on either of you because you are both happy with your relationship.

Its how I can tell if I want to spend time with a girl I like. If other girls grab my attention/I want to fuck other girls/hear them scream then the girl I'm with isn't the right girl for me so I move on and I'm honest with them about it.