Is it normal to get so jealous and should I trust this guy?

Ok so I've been seeing this guy and he snapchats me every single day without fail but I'm still not his top friend on it some other girl is (she is not a relative). I'm quite jealous I want this guy all to myself and I thought he felt the same way infact he told me himself he'd prefer it if I didn't see anyone else other than him. What do I do? And can he be trusted? He said he's not seeing any other girls :/