We start off with Anthony's mommy issues and daddy issues making him yearn for a place to belong in life warping him into thinking that it doesn't matter who you're fixated on is as a person as long as you're sincere enough in your ardor. Just as he tried to turn Therese into what he thought Liz was, the reality of who Liz really is has probably made him start yearning for the halcyon days wherein Therese brought a certain measure of class into his existence because he's a gloomy asshole who only ever wants what he cannot have. End result: his being desperately unhappy because he tries to lead the frumpy, frightened-of-life lardass with the martyrdom complex he married places that terrify her.
When one combines this with her being a superficial twit who's most in love with the feeling of being in love but not especially in love with the day-to-day crap that also aggravated and bored her idiot mother, we can see that his discontent meets up with a greater discontent of her own. By now, she's probably boring the shit out of whatever friends she has left by whining piteously about how empty her existence is and how her life is all grey and dull. At some point, she's going to alarm someone with an unsubtle hint that if the right man came along, she might bend her vows just a little just to feel like a woman....only to turn around and howl to someone about what's wrong with her that Assthony nailed his secretary because she's pleasant to be around.