Open Question: is my mom having an affair?

a few weeks ago i saw mom on a website for bisexual moms, before she quickly minimized it. I thought nothing of it. Not long after, I heard her on the phone with one of her friends. “My husband’s not usually home at this time” “I want this relationship, I want us” “I want it to all be in secret for now”. She was talking to a women. This got me scared. I wasn’t sure though, so I looked at the history on the internet, and sure enough there were a bunch of dating websites, match.com and such, along with a lot of homo and bi dating websites, all the occurred that day, the day before, and for the past few weeks. Then mom started using her cell a lot. She had never used her cell before except for babysitting. She started using it for an hour or two every day, always to this same girl. Then she started inviting this girl over, and started going out with her a lot. Mom has never done this with any of her friends before. Even when dad is on a business trip, she only talks to him for maybe 15 or 20 minutes. Even on the last night that her parents were staying over before they flew back to Florida, she went out with her friend to dinner and a movie, and did not get home until 1:30 in the morning, even though she knew she had to be awake at 6 that morning to drive her parents to the air port. She has brought this woman over, and this woman is trying to become friends with me, asking all these questions about my personal life, if i’m going to marry my boyfriend (i’m only 16), she touches my shoulder, trying to be all friendly. She brought her kids over the other day (she is married with three children, just like my mom). She had lunch with my mom, my mom’s sister, and my mom’s mom. my mom’s dad was invited, but he wanted to watch the football, and I was invited, but I refused, saying that I had homework, and was going to make Christmas cookies. I didn’t want to go. I confronted my mom about this today, and she said that it was very personal stuff, that dad knew all about it, that the websites were for my aunt (my aunt is lesbian), and saying that I had nothing to worry about. when i delayed my reply, she said “i know your not convinced. ill answer all your questions when i get back”, and then left to go out with some friends. She has also seemed to be paying more attention to dad, and is getting surgery for weight loss, bought a new van, is getting the house redone, etc. i talked to her about it and she was saying that everything is fine between dad and her, and that after loosing all that weight, she feels confident about herself again, and her friend is a talker which is why she is on the cell for a long time, and that her friend calls on both the home phone and the cell. she also said that she was only on those dating websites to find a friendship now that she is more confident about herself. when i asked about the conversation, she first turned the tables on me and asked if i was snooping/eavesdropping, saying that i must have had my ear to the door in order to hear what she said. i didn’t say that i was snooping when i saw those websites, and i explained that after hearing the first thing she said, i was shocked and misunderstood, so i kept listening to try and understand what she was on about, and when i had enough i left. she then went on saying that she didn’t remember saying any of that, and not to worry, and then the subject sorta changed to me for a while. she also said that dad knows all of this. my friend thinks that mom is cheating with this women, and so does his dad, but after talking to mom, i’m not sure. what do you guys think? please read over all this twice, so that your not too quick on deciding.