Sadly this is a common question (and most of them are about relationship insecurity).
Unfortunately we can rarely provide a definite answer: there are literally millions of apps, and a "heart" is a very common symbol used by many different types of apps (most of which are not what you fear). So unless the app in question is a common one it's a long shot that anyone will recognise it. I've certainly never seen this one before.
To be honest your best chance of getting a definite answer is probably to ask them (and hope that they don't guess why you care, as "I don't trust you" rarely goes down well).