A guy gave me his number and told me he would like to take me out for a drink. I was flattered as he was attractive and seemed nice. But I'm only visiting here for few weeks and will be going back home that is few thousand miles away in few days. More importantly I have a boyfriend. If I weren't a visiting with a boyfriend I would definitely go on a date with him but given the situation of course I won't go on a date but I don't want to just ignore/reject him. I don't know why I didn't tell him this when he gave me his number but I want to let him know it isn't his fault that he is getting rejected/ignored. So my real question is, is it weird if I let him know of my situation or am I just being a weirdo?

I know he gave me his number instead of asking for mine which could mean he just likes giving out numbers and have whoever call him back call him back and not care about who doesn't...

What should I do?

Do nothing-you have a boyfriend and like you said-this guy might be handing his number out to several girls.

You don't have to do anything, you have a boyfriend, while I understand you don't want to hurt his feelings, he'll get the message loud and clear when you don't text back.

Throw his number away, and waste no more time thinking about it. That's what I would want my girlfriend to do. No explanations necessary