Kev are you saying you're going out to eat some fish tonight?
;-)
sorry I couldn't resist
Your lady friend who is divorced and attractive is going out with you because she has a soft spot for kind, sensitive guys - it happens, possibly because she's been with a jerk for quite some time and wants to try something a little different.
Why not enjoy the evening with her for what it is and forget about "nothing more than just friends", even if it's not a date, why not pretend that it is, get in that mode of thinking, feel the vibe, feel the attraction, feel what it's like when a woman is attracted to you, enjoy it, be funny, make jokes, tease her a bit and stop thinking about the wife for one evening and don't put a damper on what could be a nice interaction with the opposite sex.
Have FUN!
(I had to spell it out just in case you didn't get that part)