How close is this co-worker of yours as far as working vicinity? If you encounter him more than twice a day in the office it's a no go. That's too close and if anything happens that's it- one of you has to go.
That being said you should find out his intentions and go if it's as friends. It's good to bond with the people you work with!
SW (Nov 22nd 2011): 333
Current Weight as of Nov 25 2015: 248
Short Term Goal: Fit into the shirts I got on my honeymoon at disney and universal in august next year when I go back to for my 1 year anniversary
Met Goal: Be a 2x Shirt, Fit in a standard airplane seat belt without the use of a seat belt extension
Long Term Goal: 166lbs (One day!), Buy whatever cloths I want to wear.
Pain is temporary, quitting is forever- Lance Armstrong #NoExcuses