An absolutely excellent article. I agree with your conclusion about marriage and feel the same way with regards to infidelity being tantamount to fraud. You do bring up an excellent point regarding fraud, though, and I think it's worth while exploring whether or not fraud does, in fact, constitute aggression.

The way I see it, fraud constitutes an act of trespass by deceit. Since the defrauded party is unable to render meaningful (informed) consent, the defrauding party is utilizing resources that he or she does not have a legitimate claim to access. Broadly speaking, this is an act of trespass, and trespass does qualify as aggression.

You can argue what constitutes meaningful consent, and I think there are cases in which the defrauded party has less of a claim to being trespassed than others (such as in the case of known serial adulterers), but there at least exist examples in which this is the case.