Is It Right To Help My Friend's Wife Zip Her Cloth From Behind

I just came across this mail, please share your thoughts on this:

I have a close friend whom I trust and in return trust me. Sometimes, I do visit him and he do visit me and in the process, we may pass night in each other place. We became addicted to this method of sleeping in each other's place and as a result; I sometimes prefer to go his place since he has more entertainment gadget more than I do plus he uses room and a parlour, while I use just a room and am not married. 

As usual, I visited him @ night after work and pass the night in his place. And now he wasn't around as he left home very early the next day, when I woke, his wife told me, he had gone to work, so, I just relax and have another round of sleep. When I woke up, she serve me food to eat after I had prepared myself for the day. 

I was shocked to receive her invitation to come help her to zip her gown from behind, since she was ready to go to her shop for normal business activity. I firstly pretend as if I did not hear what she said, & she repeated it. Then, I felt is it normal? Then, I took excuse that when I finish eating I'll come help her to zip her cloth. But, before that could happen, a lady (an apprentice) came in & help her out. 

Now my question is, let assume I wasn't eating or I had finish eating would I have help her out? Meanwhile, she's pregnant and my friend use to make a joke that he his not the father of her unborn baby (a joke I mean and he never mean that statement). Pls, help offer a suggestion or opinion as this scenario may make me to withdraw from going to my friends place as she may request me to help her zip her cloth on another occasion. No abuse pls. Just your candid opinion. Thank you!