If all else fails, you can hire a professional investigator to find out for certain whether your signifigant other is using a dating site.
Fortunately, these sites aren't necessarily as anonymous as would be adulterers and cheaters would like to believe.
Verdict: Great for people that need help with organising a great especially with the interactive Date Map which lets you track who is else is wants to meet for a pint or deep and meaningful conversation at 1am.
The USP: If you're dog-obsessed here is where you can rest assured you're in good company.
They could also be using information you simply wouldn’t know.
In that case, an option is to create your own account on one of these sites and then search for their physical attributes (age, hair color, etc) and location to see if you find a matching profile.
(Do not attempt to access a device belonging to someone else without their permission.