I wasn't going to post any personal stuff on here but what the heck, here goes...
The brother of a friend of mine who I have known for many years and who has openly pursued me in the past is a friend of mine on Facebook and I have been chatting with him on the instant message board. He is in a common law relationship, no kids, and I have been married for eight years and have three kids.
He flirts ruthlessly and I figured it was just his sense of humour to always be turning every conversation into something sexual. I never strike up a conversation with him, it is always him asking me if I am there and starting up a conversation, mostly because it makes me feel a little uncomfortable. He has starting sending me messages about what he thinks of my profile pic and status, making some sexual innuendo. I know he sends me the messages rather than posting on my wall because he is hiding it from his significant other. I asked him how he thinks she feels about our chatting and he says he knows she doesn't like it as he made some comment about me to her and it hurt her feelings. My husband knows about it and it doesn't really bother him because he knows I would never risk our relationship. I am not totally innocent about it and I know I do lead him on sometimes. Of course I am flattered and to be honest it does turn me on.
The other night he asked me to meet with him. I told him I didn't think that was a good idea. He asked why, and I told him about how I am turned on by his flattery and we should just leave it at that. He seemed very surprised by this news and that this physically excited him. He said he still thinks we should meet some time. Today he sent me a message asking when I am usually on the computer.
It is not all just flirting, we talk about how he had cancer and our spouses, politics, whatever.

So what is he thinking here? Why does he still want to meet? Why does he want to know when I am on the computer? Is it innocent or not?

I have known him for about ten years but just through his sister and we only actually see each other at parties, funerals and weddings. He has always come on to me openly in front of all our friends so I figured it was nothing serious. He likes redheads with freckles (which I am) so I assumed he was just a redhead stalker. I don't want to meet him but I don't want to jump to any conclusions. I will probably just avoid him altogether for a while. Just wondering where he thinks this is going.

He is looking for an affair.
He is pursuing you in the hopes that at sometime you will return the affection and he can fulfill the dream he is making of himself and you.
Avoid and when confronted address that you are uncomfortable being married and feeling pursued.
You have to put him back in his place. He wants to take this beyond innocent flirting.

If this were me, I would cut off contact with him and focus on my relationship with my husband.

As a lifelong incorrigible flirt, it saddens me when my favorite hobby is abused like this guy is doing. He is no longer flirting, he's serious. You need to make it absolutely clear to him that it won't ever happen. If he continues you may even have to bring in SO's.

Exactly... you have to lay down a line and make sure he sticks to it or you won't talk to him at all. And stick to your guns... He does this because he has gotten away with it up until now.

If he doesn't respect those new rules... remove him from being a friend on Facebook, its easy to do.

And make it clear... those are YOUR rules... if he can't abide by them then there will be no contact at all. He will eventually get the message.

And yeah... I think he is was over the line.

Yeah he wants in your pants, just delete him. You clearly DO NOT need to be turned on by another man, because you have a husband. It could end up complicating things with you and your husband. Especially because you lead him on. That is NOT good, DO NOT encourage his behavior, because he is blatantly disrespecting you as well as your HUSBAND and your family. And by leadinghim on at times you are disrespecting your husband. Delete, no BLOCK him from Facebook. Seriously.