Is this cheating?

Hi, I'm new here, stuck with a massive dilemma! Any help greatly appreciated! I've been with my now fiancé, over 2 years, things are great, we have our ups and downs, but all in all we're a pretty perfect couple! The fiance has to go overseas with work for 4 months, I'm ok with this, we talk on the phone, everything seems good! Now, we're 1 month in... She has met a new 'friend' out there, a guy. Originally, he is just a friend who she can hang out with, someone who has the same interests, which I'm ok with. After a few days, it comes out that she finds this guy attractive, and after some more chat, she eventually tells me she 'fancies' this guy, she likes this guy, and has been having sexual thoughts/fantasies about him, she also tells me that she has started to feel distant from me while she's been gone. Obviously I wasn't happy about this, so I subtly talk to her about it. Now she's replied that she is going to keep seeing this guy, because he's a nice guy, and she wants to stay good friends with him, even when they return back to this country, and when I ask, she tells me I have nothing to worry about. When I questioned her about it, she says she wish she hadn't told me, because now she feels bad about what she's doing, though she is continuing to see this guy! I don't want to be the guy who stops his girl having friends, but I feel like I should put a stop to this and/or end our relationship if she has been unfaithful! Am I over reacting here? It sounds a little fishy to me, what are people's thoughts? Thanks

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