Why would my girlfriend hang round with a guy she knows wants to have with her?

We've been in a relationship for around about 6 months now and I moved away about 4 months in so I just see her on weekends now and in the last 2 weeks she's hung around with this guy she didn't know very well and only talk to on msn occasionally. In the first instance, they just walked around for 5 hours talking. He talks about how cute and pretty she is all the time and has a new pet name for her like every 10 seconds. So I started to get a little suspicious. I know she wouldn't cheat on me but I can't help but feel like this guy is lined up for her like something to fall back on if it doesn't work out between us. She's also been less affectionate with me lately and when I told her so she went straight to him on facebook and asked if he thought she was unaffectionate to which he replied "you are incredibly affectionate. half the time we spend together is spend hugging, snuggling and holding you". You may of guessed that I hacked my own girlfriend...pathetic right? I was suspicious it was killing me I didn't want to do it but my suspicion was too great. So she says it's not like that they've only hugged a few times but I have no idea why the dude would say that if it wasn't true. Do yeah the second instance is happening right now as I type this she been out drinking with him and his friends for like 6 hours and said she was going to be home by 8 but then lost track of time and now has no idea when she'll be back blah blah I KNOW I'm paranoid. paranoia is a natural feeling but I know it shouldn't be to this extreme of total anxiousness and worry. So I just want to know why she would want to spend loads of this time when she is fully aware that he worships her and would do her in a second. Thank you.