How can I stop myself being jealous?

The guy I've been seeing for about 2 years(it's complicated😒) is at university about 2 hours away from me so I don't get to see as much as I'd like to. I've lost trust in him before and now whenever I see pictures of him with girls I get really jealous and when I tell him he says they're just his friends and I'm being silly. How can I control my jealousy and paranoia?😞