Pam - as others have said, unless you’ve had the discussion and agreement on exclusivity, then it’s best to assume you’re not exclusive. People think they can do whatever they like because, in reality, they can.
The thing here is to have the (admittedly awkward) conversation in person.
Say you got an alert on tinder that someone wanted to chat and you just weren’t interested in them, so you thought you’d delete your profile and the app. But that made you want to check you were on the same page - would he be willing to do that too as it’s been five dates in three months, but you see that as something you want to concentrate on.
And watch his reaction. If he’s hesitant, it means he won’t do it. If he blusters, it means he’ll probably go back online. Ideally he’ll say he’s already done it, or that of course, he’d assumed exclusivity too, so he’ll do it now.
Online dating is like a sweet shop. People know they can find a new date fairly soon, so they compare and contrast and if you have an argument, some will jump straight back into it.
Even on here, people say they have multiple irons in the fire, are dating several men at the same time, even in some cases sleeping with one and still dating others. It’s not exclusively male behaviour, it’s just modern dating. The old rules still apply though. Say you want exclusivity, watch how he reacts, if he won’t do it then dump him. If he hesitates then take a big step back emotionally and decide whether you want to continue with him.