I ’31M’ Caught Fiancé ’29F’ Sexting her gym trainer. Do I call off the wedding?

This is 24 hours fresh, and so raw. I met my Fiancé around 2 years ago at a community college in So Cal. We were classmates for three months until I asked her out for coffee. On what I thought was our first date, she casually mentions that she has a boyfriend living back in her home country. I found it very odd that she'd never mention him in class, on our phone calls, or on our group zoom meetings. I took the news okay, and just went forward with our beach day and bike riding. When I dropped her off later, I was thrilled at how well we hit it off, but disappointed that she was taken. I left it alone and stopped pursuing her. 2 weeks later she invites me over for movies. I go, and she tells me she broke up with the guy back home. I made a move, and we eventually fall in love.

This relationship went on to be the best relationship I've ever experienced. We developed incredibly trust and chemistry and were totally compatible. Sexually, everything was amazing, and intimacy, was completely there. I developed incredibly strong feelings for her, and for the first time in my life, I found someone I could put before myself. She did everything in her power to make me feel appreciated, special, loved etc. As we get to know each other I soon find out she's bipolar and had experienced very serious episodes in her youth, as well as a suicide attempt. We work through any future episodes, and I put it upon myself to guide her mentally. It's tough work, and there are some mental episodes along the way, but we get her on medication, and it subsides.

Early on she starts dropping marriage and baby hints, and this really escalates to where it's obvious where she wants this relationship to go. We begin to have discussions about starting a family, and even talk about how we could make it happen. At the time, I am a little surprised at her grand vision of babies, marriage, and a house. She painted it like something out of a movie, and it seemed slightly unattainable for where we were in our lives as college students working part-time jobs. I eventually catch up to her vision, and I propose in February. She accepts joyfully.

7 months later, here we are. We're planning a wedding. By summer we have a venue booked, a photographer, and a DJ. Also, by this time we've made two trips to Central America to visit her closest friends and family. I receive all of their blessings, and they take me in as their family. We make the decision to have her stop taking her bipolar medication in order to prepare for a baby. She claims it would be dangerous for the pregnancy. Here comes August. Oh man. Up until August everything was fine and moving along. She mentions that she wants to start working out again and join a kickboxing gym like she did back in her home country. I go with, and we do a class. She loves it. She looks super empowered. The main guy there is super respectful, and we convince her to join. I'm thrilled for her. She's finally getting exercise and is super excited about fitting her new wedding dress. This is an amazing outlet for her mental health, and she looks happier than ever.

Then things get weird. She starts going 6-7 times a week. Sometimes even two classes in a row. She starts missing morning work, spending less time with me, and even leaving our dog at home alone extra hours because she wants to kickbox right after work. I begin to get upset with her for leaving the dog alone all evening and her becoming less accountable.

3 weeks ago, she casually mentions a trainer who I'll call "C". He offered her self-defense classes, but that it had to be a secret from the other trainers. She asks me if she can go, and we have a very serious discussion how uncomfortable this makes me feel, and how I will consider this crossing a serious boundary if she sees this guy outside of gym hours. She responds with, "what about if my sister comes too? Is that okay?" I give her the same answer.

Now my antenna is raised, and I'm starting to piece things together. She mentions compliments he makes to her about her figure and body transformation, and how lucky I must be to have her. He's fully aware she's engaged, and all of her girlfriends there have met me. She seems thrilled at this guy's attention and completely naive to his motive. (Without making excuses for her, she's a very classy dressing girl who doesn't wear makeup and I don't think she's used to this type of flattery) Anyways, I then notice her not doing the little things she'd done previously in our relationship. She becomes slightly more distant, and I notice her new strange phone behavior. She does things like taking it with her everywhere and becoming nervous when I'm around it or when I'm changing a song. I was terrified to dig deeper, but I did anyway.

I eventually invite myself to the Sunday morning class. "C" is there. He completely ignores us and keeps his space to avoid us. This was highly concerning because I knew that they were at least friendly. I catch her looking at him 3 times.

We go to breakfast later, and I see her anxiously checking her phone. When there's a message she jumps to respond. I can see the "C" at the top of the phone. I quietly make the decision to go through her phone later that day. I realize how bad she is at deception and how obvious it's become.

Later when she jumps into the shower, I go to her iPad and open up her messages from the iCloud. Holy shit. There it is. Weeks' worth of sexual messaging. Talk of sexual fantasies, sexual songs being exchanged, and the excitement about the possibility of future sex. She's messaging him what she did that morning, describing things she's doing with me, while flirting with him in the process. Truly just gross messaging from someone I didn't know was capable. I don't discover any evidence of actual meetings, just lots of "what if's" and, "how about this". She not once rejects his advances. The worst part is she sends him pictures of herself in dresses and pictures of her holding our dog, dragging everything I hold dear into this sick fantasy. I send him a message from her phone saying it's me and I know everything that's been going on. I then confront her. She's speechless. I hear a million "sorrys" and, "it means nothings", "we were just flirting", she says. I pack my stuff and leave her apartment.

This is now the day after, and I've received paragraphs of apologies.

In conclusion I am seriously lost at the moment. My brain is saying to end the engagement and call off everything, but my heart wants to make this work. Right now, we're in a break, and she's messaging me anything to get me back. I've given this girl everything, love, respect, time, attention, intimacy, etc. and I feel completely disrespected. My family is devasted but totally behind any decision I make to call it all off. I'm truly shocked and betrayed that this was going on right behind my back. We had $7000 invested into a wedding venue, as well as her family from Central America getting ready to make the trip to California. We had sent out invitations and were expecting 100 guests. Everything is broken. I feel empty. How could she let this happen in such a short time? How could she risk throwing it all away for this dumb move? How is she going to explain this to everyone?

I am totally lost right now. Comments, concerns, ideas or advice is needed.