Relationship rollercoaster

Okay, so me and my girlfriend have been bestfriends for 5 years and we always had that conncection, neither of us really did anything about it.
Anyway not long ago we did and now we have been together for 6 months, which i know isnt long. Due to my past relationships i find it hard to trust people, i have been lied to, cheated on and abused, i know she would never to that to me, but she says i dont show enough affection or love towards her, which sucks because i think the world of her, im just scared of getting attached, how can i prove to her that i love her and think the world of her?