That's just not how it went down. Terese was not jealous of Lauren at first. This is a quote from Perfect Blend:
http://perfectblend.net/neighbourhood/bio/willis-terese.htm
Terese started to become insecure after finding out about Paige, but the kiss between Brad and Lauren in Adelaide is what really caused their marriage to start falling apart. That kiss was definitely hot, heavy and flirty!
Terese has behaved badly at times and that certainly didn't help the situation, but blaming her for the breakdown of her marriage doesn't make sense.