Hey, guys. I've been with this girl for about two years and we've been living together for half that time. Some behaviors and signs have come up that make me think she might be cheating, and I'm wondering what you guys think.
What first got me suspicious was the sudden appearance of bruises on her upper thighs -- small, finger-sized bruises -- some of them in a row like a hand grabbed her. These are in places where I don't grab her when we have sex. When asked about them, she would either make up an excuse, like bumping into things, or claim no knowledge of how they got there. She says that she bruises easily, but this is a sudden change and I never saw these kinds of bruises before. I caught her trying to hide a new bruise on her ass, and she said I did it when we had sex, but it wasn't in a place that I even touch her.
Around the time these bruises started appearing, she suddenly began buying sexy underwear and lingerie (no interest in this before), getting in shape, dressing more nicely, and tending to her appearance better.
She started doing different things in bed out of the blue, but normally she was extremely reluctant to be adventurous or experimental. Her sex drive seemed to increase as well, and she wanted more sex more frequently.
She started biking to work, showering there, and working more overtime than usual.
At first, I asked pretty docile questions about the change in behavior, and she was extremely defensive about it. As the behavior continued, I came right out and asked if she was seeing someone else, and she swore that she wasn't and would never do that.
Her co-workers are really weird around me: they keep very grave expressions, body language, and tones of voice, and they don't respond to good-natured conversation. They find excuses to avoid me in social situations.
Am I being paranoid, or do I have reason to be suspicious of her cheating? If so, how to I root this out and get it into the open?