I, too, was unsure of the "CaptivePortalLogin" system app when I saw it running on my phone, but when I typed "captive portal" in my browser's address bar it listed a website I was at recently (in my case "Easyhome Captive Portal") which reminded me that I had used the free wifi at Easyhome Furniture which indeed had a captive portal "do you agree to the terms of our free wifi" page.
There would be far easier ways for a nosy person to monitor what you're doing on your device, including hidden apps that might be installed.
I had a friend who was concerned about her abusive spouse monitoring her. I initially dismissed her concerns but it turned out she was right (which I learned when the jackass called me from a spoofed phone number -- another app that was surprisingly easy to find/use -- which I confirmed by called him back spoofing the local police phone number, telling him his hacking activities are being monitored... Worked like a charm; he promptly left town!)
If you're concerned about that I'd suggest:
- factory reset your phone,
- create and use a new Google account (don't use the old one as backup email!),
- don't restore your device from a backup,
- pick a new screen lock code or use fingerprint recognition if possible,
- set the screen to lock quickly when you're not using it (sleeping/bathroom/etc)
- stop giving out your passwords and lock codes to ANYONE, EVER, and most importantly,
- find a new spouse (or better yet, stay single for a while and ask yourself why you jump into relationships with untrustworthy people.)