I don’t know whether to trust him?! Please help

So two years ago I moved here for my boyfriend to persue his policing career. For the first 6 months he was living at the academy and I only got to see him on occasional weekends.

Anyways, last year a girl added him on Snapchat and I found out she went to the academy. He pretended he didn’t know her and after I did some digging I found out he had deleted her Facebook friend request when he was at the academy (which he never does, he always leaves friend requests even if he doesn’t accept)

She tried to add him AGAIN on Snapchat the other day and AGAIN he said he didn’t know who it was and because I remembered the name I told him and he was trying to gaslight me and say “no it could be anyone I don’t know if it’s her” .

He also said he has never had any real interaction with her other than “hi” when they walked past each other . She wasn’t in any of his classes either and she’s mutual friends with his friends he was closest with in the academy. I’m just finding it really hard to believe that he had no real interactions with this girl

He says nothing went on and there’s nothing to worry about but I don’t know if I should believe him !! We have a child together and engaged , there would be a lot to lose if I chose not to believe him