SawTheLight has a point. I misread your post and saw he's back with an ex.. It depends what your gut feeling says on this, only you know how genuine this relationship is. It might be for revenge or so he keeps distracted from you, or it might be genuine.. Go with your gut feeling, as that's never wrong. Nobody can answer except you. I will say that when they said that there is nobody around him and you corrected them that he is with someone, most psychics automatic responses are "well, it's nothing serious". Most don't like to admit that they got something wrong, and most don't admit that a man's with someone else and he's genuinely happy and in love with her.
Which Melody are you on about?
You nailed it!! I also want to add I had something similar years ago when my ex at the time cheated on me with another girl. My gut instinct was telling me he was seeing someone, he became distant and annoyed with everything I did. I asked a few psychics if they could look into my situation and most said he wasn't with anyone else. I ended up doing a bit of digging around on social media and I found pictures of him with this girl so my feeling was correct.
I decided to have another reading and sent the psychic a picture of them together so I could double check things because I was seriously indenial at the time. The psychic ( I forgot her name) pretty much told me he was in a sexual relationship with this women pictured and she was someone he knew from the past.
The woman in question was his ex from awhile back so there was a connection already established she wasn't some random girl so yes only one psychic could read the situation with accuracy, maybe the picture helped to strength what she saw.
I do know some psychics aren't able to pick up on a third party if they is no emotional connection so it could be that. Like the others have said, only you know the most information about your POI, has he mentioned this ex before? It might give you an idea if he is still pining for her. Is there anything on social media of them together like a picture, you could try sending one to a trusted psychic and see if you can get anything more to explore that way?