You can certainly ask a trusted friend to deliver that news (as I think you said above you were going to do), but your wife may STILL think you are just behind its delivery in order to be "controlling." Ultimately, she is responsible for her own health, and certainly so after the friend tells her. All you can is protect yourself by not having sexual relations with her, and by insisting upon a full-panel STD test (and then repeated, six months later) and a copy of the results shown to you if and when you two ever reconcile.
As for the cost of a trainer, you should offer to continue to pay for her personal training, but NOT with that trainer. If she won't agree to that, then stop paying for the training altogether.
