Re: a friend is tempting me horribly
Watching porn featuring a female friend is not the kind of thing you should do without your wife's consent and the consent of the female friend. It's one thing if a buddy shows you a picture of his woman or whatever, I've had that happen several times and it's really not a big deal, but doing this is a real big deal. You will be crossing a major line into dangerous territory. Are you willing to destroy your marriage over this?
If you're just curious about seeing a woman engage in particular acts you can find porn on the internet that doesn't feature a woman you know, it's not like it's hard to do.
Also, porn isn't nearly as sexually arousing when it's a woman you know who isn't and never will be your sex partner. It makes it too personal, it becomes about finding them sexually arousing and that's uncomfortably inappropriate to the point of distraction. Instead of "wow, his girlfriend has such sexy tits!" it turns into "yep, that's his attractive girlfriend with no clothes on". If that's not how things are for you with this female friend you need to get a handle on it. You should be able to see any of your female friends in a sexual context without finding them personally sexy.