I'm being wooed by a City Gent! ?

I recently found a job in the city of London. I'm 25, I have a boyfriend we've been together about 5 months and its been so special so far. And I want more special times! Treats me so well, gentleman and he's very kind. This is why I feel so awful. I had a customer in the "up-market" bar I work in and that was him. Instantly I was attracted, he gave me his business card and I sent him a txt saying sorry I have a boyfriend. He txted but no reply from me. I for some reason agreed to go for a drink (JUST a drink). Was fine. But now I can't get him out of my head what have I done?! He wanted to kiss me but I refrained. He wants to take me out at the weekend but I haven't given an answer. A colleague of mine says "do it once and get it out your system". A part of me is seriously intrigued but I know this can cause trouble. I don't know what to do!!!!!!