Question on Dating

Hello All,I've been out of the gayting (get it?) scene for a couple years now and recently decided to put myself back out there. The few relationships that I've been in all started as friendship and when we crossed the bridge to be "official" it was soon after we started doing "boyfriend things" (too many quotation marks? definitely). I've never dated anyone from the get-go so this is kinda new for me.I started talking to a guy online a couple months ago and about a month ago we met up for the first time. The other night he told me that he is seeing other people and thought I should know. Some of my friends are telling me this really is unacceptable and I should cut it off with him, and others are saying it's not that big of a deal. What's your take on this? I really like the guy, but it's hard for me to think about him with other people. Also I've always stuck with the "no sex before monogamy" rule which would be pretty hard to stick to in this type of situation.So r/gay what do you say? Stick it out with the guy and see where it goes, or cut it off before I'm truly invested? Thanks in Advance!