I've been on both sides of that coin.
Eight years into a marriage--only the first four of which were good--I felt so much distance between my then-wife and me. She talked... a lot. A whole lot. I... did not. More accurately, could not. I felt isolated and unimportant, not just because of that, but it had a lot to do with it. My job moved from an office just around the corner to the other side of town, and I met a girl on that side of town who actually listened to me. It felt so good to feel like I mattered to someone, I felt almost high after I would spend time with her (in fact, I often compared her to a drug). I spent more and more time with her... talking, texting all day, even meeting up when my then-wife was at work. I guess I got careless, and we ultimately got caught. My marriage ended shortly thereafter, and the girl--who knew I was married all along--wanted nothing more to do with me after that. I felt guilty, and still have gut-wrenching guilty feelings to this day, but the amazing feelings of being listened to and having someone to actually communicate with did help me realize that the love in my marriage had changed and it just wasn't working anymore.
A while after my marriage ended, I met an amazing woman locally. She was the polar opposite of my ex-wife; my ex- was short and stocky, and she was tall and beautiful. My ex- flunked out of community college (because she wouldn't stop "telling the teacher how wrong she was") and she was finishing up her master's degree. My ex- had a low-level hourly job, and she was a senior employee with the government. She knew how to listen, and our communication was incredible. We were "together" from our very first date, and we were as tight as two people can be very, very quickly. Our relationship went on--with typical ups and downs, but mostly amazing ups--for two years, until one night she left her phone at my house. She had been as lovey and doting as always, but something felt "off," so I decided to check out her phone and see if anything was going on. It was. I won't go into detail, but someone we both knew was pushing her hard to get together for sex, and she wasn't turning him down. She made several comments about how I wasn't satisfying her, blah blah blah. I confronted her, and she owned it immediately. She swore up and down that they never actually met for sex (I believe that), and that she would never do it again. This woman is the love of my life... Im in my 40s and have never met anyone who makes me feel the way she does... so I forgave her. We're still together, and I strive to get past it... but every time she gets a text, some little piece of me wonders... and probably always will. She tells me how much shame she feels from it, how she will never do it again, how I'm the only one she wants to be with, and so on... but if I couldn't trust her then, how can I trust her now?