If you're planning on acting on it at a later date, please have the decency to break up with the current beau first

This screams bad idea to me

Oh no, this is not good. Don’t cheat on your husband, think about how you would feel if the roles were reversed. Don’t do it. Think of your husband’s feelings and of your children.

I’ve been there. Once you go down that path there’s no turning back. Cheating is addictive, as you described it’s like being drunk when your with the other person. It causes an addiction and eventually you no longer feel the guilt you fall deeper and deeper into the affair.

Remind yourself that this is the sort of man that makes a move on a mate's partner of 8 years - bit of a turn off, isn't it? Now imagine that he meets someone else that turns him on and they have electric chemistry - what's to stop him acting on that too? Clearly not his respect for his mate or the 8 year relationship he's been in.

You have 8 years of growing and deepening your connection with your partner that you really don’t want to jeopardise for a sexual fantasy because of a chemistry reaction. You are around the “7 year itch” stage where relationships are less about spontaneity and more about the cycle of just living together. I was given an opportunity like this but realised that an affair would not lead to a permanent relationship with this person, and it would ruin my relationship with my current partner. It would also ruin their friendship and I expect they would eventually make up and I would be left on the outs. The only reason his friend became so obsessed with me in the first place was because my partner boasted about me to him, and once I saw his friend as the type of guy who was just jealous and willing to dump on his best friend, he stopped being so attractive to me. Good luck with everything.

Just remember that the grass is not always greener on the other side

If you love your partner and want to remain with him then you need to remove yourself from this situation. If the bloke comes over, make sure you're not there. Don't be alone with him etc.

Maybe it's the thought of it being forbidden, that makes it more appealing & attractive, especially when you fantasise, everything is wonderful.

If you don't want to take it any further with the friend, try & distance yourself physically & emotionally. Start thinking unsavoury things about him & turning the fantasies dull & boring.

You have a good relationship & share children don’t risk that for some sex. Distance yourself from that guy NOW. Avoid the temptation, turn your head back towards your guy, without that other dude around hopefully special feelings towards your man will blossom again.

If I had feelings like that for someone else, I’d be truly questioning my love for my husband.
You actually shouldn’t have feelings like that if you truly love your partner.

Another thought - Turn it around - how would you feel if it was your partner feeling those feelings for one of your friends? Would you accuse him of cheating?

Do you feel the same way about your partner? Is everything at home okay? I ask because it seems obvious that you have a connection with this other person, that obviously make you feel good. Its good you didn't act on it, however much you wanted to however I suggest you look into your heart and try to work out if you are happy in your current relationship. If you are maybe distance yourself from his mate. Maybe talk to your partner about how you feel what you need from him if something is missing.