"a plaintiff must prove that the defendant’s actions were the sole, proximate, cause of the break-up of the marriage."

Doesn't sound like he is the reason the wife has decided to call it quits.

Illinois law for alienation of affection is limited to actual damages.


(740 ILCS 5/2) (from Ch. 40, par. 1902)
Sec. 2. The damages to be recovered in any action for alienation of affections shall be limited to the actual damages sustained as a result of the injury complained of.


(740 ILCS 5/3) (from Ch. 40, par. 1903)
Sec. 3. No punitive, exemplary, vindictive or aggravated damages shall be allowed in any action for alienation of affections.
Alienation of Affections Act

Another interesting article:

http://www.illinoisdivorce.com/famil...affections.php