My (23F) boyfriend (25M) of two years told me he's bisexual after I caught him in a gay sex act, and he expects me to "get over it". How should I proceed?

I was in the, "don't ever know" phase of my relationship with C until a few days ago. We were on the same page about a lot of things, and I was considering proposing soon. So, I thought I did.<br><br>C has always been somewhat...prone to lying. I would find out almost every day for the first year of us dating that he was lying about almost everything. He told me he was at work, but was really out with friends. Or, he told me he had a bad day and just came home, but really he was out at a bar drinking, but didn't want me to know about it. It took a toll on me, and I was to my wit's end. After the first year, I told him I couldn't be with someone that lied so much, and that was that. Except he changed. He started telling me the truth. He was transparent in a way he had never been before. He told me all about his day at work, what he did with his friends, what he did on his own. And things were finally good.<br><br>That's why, when I started noticing C had started lying again after being with him for a couple more years since our first big fight, I was worried. I knew it was a bad sign. I even thought he might be cheating on me. But, he always lied about the same things. He always lied about work. After a couple of months of me noticing he was lying again, I decided to confront him about it. I sat him down and asked him if he still felt like he had to, but he denied ever lying before, including the times I found out. I let it go and moved on.<br><br>A few more months went by and I would notice that he was still lying, and I continued to confront him. At one point, he even told me he was going out of town to visit his family for the weekend, but when I saw him post on Instagram with his friends, and he denied ever telling me he was going to visit family, I started feeling like I was going crazy.<br><br>Fast forward a few more months to now and here I am, writing this post. A few nights ago, I was feeling in the mood, and it was pretty late (around 10 o'clock) so I thought C might be half asleep. I snuck into his room and started giving him a lap dance (he always loves it when I do this to wake him up, even if he's dead tired). He was sitting in his office chair, and the desk was to his right. I started grinding on him, and he slowly started coming to, moaning in pleasure. But, when he opened his eyes and saw me, he let out a shocked groan and pushed me off him. I fell to the floor, and when I sat up and looked at him, I saw that he was in the middle of a video call with another man, doing a sexual act. The man saw me on camera and smiled, and C immediately closed the stream. When I asked him what the hell he was doing, he told me he was just "curious". He said he wasn't doing it for long, but didn't want to tell me because I would think he was gay. I was so distraught that I just left his house in tears. He tried to text me and call me, but I didn't answer. The next day, he came to my house and told me that it didn't mean anything and that he was just bored. He said he never had a gay experience, but that he was "curious" (that word makes me want to scream). I was still so upset. But, when he broke down and told me he was bisexual, I broke down too and cried with him. I told him I would stand by him, but only if he told me the truth about what was going on. And he did. He told me that he had met the man on a dating app over a year ago. He told me they met in secret and had sex, and that he enjoyed it. He said after that, he felt guilty, and they agreed to stop meeting. But, they continued talking via text and video calls. He said he never loved the guy, but that the guy told him he had feelings for him. He told me that after our fight over a year and a half ago, he realized he needed to be honest with me about everything. He said it felt relieving to be transparent with me, and he realized that lying was a terrible habit and he needed to stop. He said he felt bad keeping his bisexuality from me, which I understood, but why did he keep the other stuff from me? He told me that he didn't like lying, and he didn't want to do it anymore, but he didn't want to tell me that he was meeting the guy because he knew I would leave him. He told me that after the first time they met and had sex, he agreed to meet the guy whenever, but only for sex, and only in secret. But, he never loved the guy and didn't care if he was with anyone else. He never told me about it, and he never intended to. He told me that he was going to keep meeting the guy in secret until I found out, like I did. He said that the guy didn't want him to tell me, because he didn't want to lose him. He told me that he was going to kick the guy out of his life for good, and that he was never going to cheat on me again. But, I'm still so hurt. He told me to just "get over it", like it meant nothing. He told me that he would do anything in his power to make me comfortable, and that he still loved me. But, I don't even know if I can look at him the same anymore, let alone be with him. He told me he was going to delete the guy's number from his phone and remove him from all social media, which he did right in front of me. What should I do? How can I ever trust him? Even if he's telling the truth this time, how can I ever be sure?<br><br>**TLDR:** After two years with my boyfriend, I caught him in a gay sexual act with another man. He told me he was just curious, and it didn't mean anything, then revealed he was bisexual. He told me he was going to continue lying to me and cheating until I found out, but that he's going to end it now and kick the guy out of his life for good. How can I ever trust him again after all the lies?