My girlfriend has changed

I have been with my partner for nearly 3 years I am 19 she is 18. She recently went on holiday with her friends and when she came back she was a different person, very distant and the love seems to have dissapeared from the relationship. We have talked and nothing has changed. She made friends with some lads (one in particular) and they keep in touch however she has put a lock on her messages which I don't like as it makes me feel like she has something to hide. I wouldnt have a problem with her being friends with a lad but when it is secretive it gives me doubts. I love her very much but im just not happy i don't know what to do.

hi paul,you are still both young were you happy she went on holiday by herself,are u going away with your mates?obviously you think something went on with this boy she met have you talked to her about him ?is she putting your mind at rest ,what does your gut instinct tell you,and if she has done something could you forgive her ,as for locking her phone it does sound like shes hiding something.the thing is it will eat you up inside if you cant put it behind you and move on,do you think your relationship has run its course ,does she?talk to her again and see what she says.

thank you for the advice it really helped I have spoken to her and we had a long talk my gut instinct is that she hasn't cheated and I gave her the option of ending the relationship but she didn't want that so we both agreed to give it another go. What do you think? thank you

hi,glad youve sorted things out its good to talk things thro,maybr now you can move on and be happy. i to have been thro my hubbys phone and followed him as i have caught him out b4 but unlike you i cant forgive or forget and i wont stop till i catch him ,he might be getting more clever or hes innocent we,ll see take care and be happy.