should i be worried about cheating?

we've been together for almost two years and he's always been really comfortable with me having his phone , and vise versa but this last month he told he'd been talking to his old friend (at least he didn't hide it from me) and ever since he told me this i have not been aloud to even touch his phone! he gets so angry when i grab it even if i only want to change the song that's playing. i try to make conversation about her to get to know her a little better since they're old friends and maybe we could all get along .. but every time i bring her up he gets furious and starts talking about how i don't trust him. he's never gotten like this about anyone i don't know if i should be worried about her or not?