Before my H had his affair I had the oppertunity to do the same. At that point in our R things were bad, I will addmit to going out and having drinks with this guy but that is all we ended up doing. But I could have very easily, if I had known at the time about what was going on with H, fell into the affair and hard. To this day I really don't know what kept me from going any further than what I did, maybe morals, but I am glad that I didn't. But after things cooled down with the other guy I realized how much I loved my H and did not want to lose him over something stupid like an affair. When I found about my H's affair I was kind of mad at myself for not going any further, but on the other hand I was glad that I did not, I had nothing to hide from H.
All I can tell you is to stick to what you were taught at home and you will be just fine, you know morals. I know they get in the way sometimes but they do keep you out of trouble.
Oh one more thing- It is hard to consentrate on two relationships at the same time, wheather it is just in your head or not. I know that you have an emotional hole but be careful with what you fill it with.