So my boyfriend and I rented a room in some hotel in our city to celebrate our valentine's day. (this happened on feb 15) While we're on our way to the hotel. He is telling some things like what's it like inside the hotel and something. So I asked him "Have you been there before?" he paused and later said "That question made me think on how I know those things and I remembered that I saw the hotel when I was passing by back in highschool. Blahblah" he was saying that it will be his first time there and he just guessed it based on the structure of the hotel. I just shrugged it of since I trust him. Then this day, I don't know why I looked into his convos in messenger (especially in his ex) and there, I saw there chats on how they feel pleasured on what they did back then and they checked in at 3 hotels (including the hotel that we went to) and how frequent it was. I know it is the past so I should focus on the present. But I just feel betrayed. He said that it was also his first time to do those kind of things when we were gonna do it on the first time. He could have just tell the truth instead of lying to me when I asked him some questions before. He said he will never lie to me. I don't know what to react for now. I feel cold and numb. What shall I do in these kind of situation?

Sorry if some grammars are incorrect. English is not my first language.