Hey Lisa 
Oh, I feel for you! I’ve been through similar heartache, catching my ex’s late-night glow while texting someone else (discovered those messages at 2 a.m. with trembling hands and a cold cup of coffee!). Some classic signs are: being emotionally distant at home, hiding or obsessing over his phone, and always having that special “spark” when she’s around. If you’re close, maybe share your observations gently—sometimes they don’t realize the impact. Protect your own energy too, maybe treat yourself to a cozy coffee break.
Sending you love and warm hugs 
If you (or his wife, with her consent) ever want clarity, mSpy can help uncover hidden chats: