Did I cross a line because I contacted on old girlfriend from 25 yrs ago on FB?

Its hard to say. I mean how interested are you in finding out how she's doing? Hopefully you still maintain a stronger personal interest in your wife. Show your wife how much you love her by still being interested in her and take time out to enjoy being with her.

Depends if you have a motive or you just want to see what's up

wilderheart hit it on the nose... if your intentions were not to 'wander' from your wife then you should confront your wife and communicate that very clearly. If you truly are sincere that should come through. If your wife simply cannot put her mind at ease ask and explain why to your long ago GF if it would be alright for your wife to contact her.

How close were you with this GF? If you lived with her, yes, you crossed a line.

Your wife sees this as emotional cheating, which is the worst kind. Sexual dalliances are easily forgotten, but emotional involvement is deeply wounding.

No, but I can see why she would be mad.

Your wife is overreacting. It's not like you secretly tried to do this behind her back.

I don't think you crossed the line. You're an adult but you should have probably discussed the contact with your wife before you did it. It's not that you needed her permission it's that when you give your freedom up to someone you change the dynamics of your life and there are consequences for things that you do that would not normally be a problem if you were single. She has jealousy issues obviously. If my husband did such a thing I wouldn't care because I know where he sleeps every night and I am not an emotionally weak, dependent person worried about another woman stepping in. If there was anything to this I'm sure you know the best thing would be to say so and move on with your life..

No, she is overreacting.

It sounds as if she's overreacting. Maybe it depends on what you said on FB, I don't know.

Yes you did. I've done this exact same thing and was caught by wife and had some explaining to do! :-)
You say (like I did) it is not that big a deal, doesn't mean anything. But the fact that you had some curiousness suggests that consciously/sub-consciously you were seeking something. Maybe the warmth of friendship, just some talk.. or some flirtation or more?! What if she responds and says yeah I'm doing great. Are you going to now move on and never peek at her page again? Or if you find out that she is divorced. What's next?
I did it not to cheat, but there was something in me that had this desire to know more I guess. Ideally you shouldn't care unless you hear from someone she is going through hard times or something like that. But we don't think with our brains, do we? ;-)