Help I need serious advice

Okay so my bf has had a really close friend who’s a girl and a few years ago before we were together they got together one night but nothing major, they never spoke about it and carried on being friends, me and my boyfriend have been together for a year now and he was always texting her which was fine he never hid it from me but recently he’s been hiding the fact that he’s texting her and won’t let me see anything it’s so strange and he acts really weird about her recently so I got paranoid and read through his messages and I saw texts from when me and him were on holidays together last week saying that they both missed each other a lot

What do i do am I over reacting?? I don’t want to sound like a psycho