Is it still infidelity if they say...

[Sugar and Spice]

W2G,
Sorry that you are in this situation, but this is an excellent place to get support and insight.

What kind of relationship do you actually have? Is it a friendship or a co-parent relationship or does he lead you to believe that things can be repaired? I would need to have a better idea of where things are to really give you an opinion.

He claims that I am still his best friend.

If this is how he treats his best friend then thats kinda scary. From personal experience as well, trying to be the "best friend" of the man you are married to while he is cheating on you is a very painful and counter-productive path.

You say that in your head you know its over, but from what you have posted it sounds like he is giving mixed signals.