It’s so nice to have people pay attention to you. Especially someone who you are attracted to. Right now a little office chitchat is ok. You are not married after all. However, if you love your boyfriend I would keep it light and in the office only, no happy hours or business lunches. Too much room to stray. If you’re open for the adventure, I’d let your boyfriend know what’s going on so he can decide if he wants to stay or not. Unfortunately, you wont be able to keep two men for long.