Married, but Maybe...

Question…is it ok for married people to make new friends of the opposite sex? This question comes from the past weekend. I met this guy that I thought was attractive. We chatted and danced for a bit then I saw he had a ring. So I said “so you’re married?” he says yes and asked me the same. After that I was prepared to say goodbye and walk away when he asked if we could have lunch sometime. So this got me to thinking all kinds of things. When it comes to marriage, where is the line? Is it ok for a married man or woman to accumulate new friends? If so what’s the procedure. Is it cool if the other spouse knows about it? Are you bound to only the friends you had before the relationship? Are you only allowed to make new friends of the same sex? Or only new couple friends? Is it possible for a married person and unmarried person of the opposite sex to be platonic friends? Do you think he would have gone home and said “oh yeah honey, btw I met this really nice girl today, we’re going to go grab lunch next week”. Or would he have kept it from her? The line just seemed so innocent coming out of his mouth like it’s not the first time he’s met someone in such a way. It wasn’t sneaky or adulterous but would it end up being sneaky and adulterous? Or could something seemingly innocent like lunch open the door for something inappropriate to happen and therefore such things should be avoided?