<human>: Can you summarize the given text in a few sentences?

My girlfriend and I live in a nowhere town in Layton, Utah, and have been together for just over a year. Recently she's been talking more and more to a mutual friend from work, constantly texting him whether or not I'm around.

I've known this friend for a very long time, and I have no reason to doubt his character, and from what I've heard he seems to have been a real rock to her lately when she has had a problem I haven't been able to solve. 

However, I do worry sometimes as I've seen, just accidentally glancing over her shoulder, that a lot of their text conversations end in "love you"s and hearts, which I've brought up with her - her response being that she totally understands why I'd be worried and that it's our friend who started this and that it's totally innocent: meaning she didn't want to be impolite (she reassures me all of the time that she doesn't find him attractive, and that I am the "only man alive" she is attracted to, as she had only had girlfriends before we met). In addition she sometimes stays at his house when I am away on business, something we have talked about a lot; I didn't want to break up their friendship and so have requested she ask me if she can stay the night at his. This isn't so I can say no and control her movements, it's simply an act of courtesy that keeps me at ease.

However, when she actually is there, she's suddenly unable to reply to any messages I send her, as her phone is either out of battery or not working. I'm worried that the wool is being pulled over my eyes, but I worry even more that I'm just a really jealous guy who can't deal with my SO having friends of the opposite sex. Our relationship is otherwise wonderful, it's just this small thing that makes me uneasy.
<bot>: Girlfriend spends a lot of time with mutual friend including staying over at his house, but does her best to comfort me and assure me that they are simply friends. Am I right to be anxious or am I simply a jealous person?