Your client/friend is feeling very lonely and looking to fill that gap in his life, as you are showing him attention he thinks you are interested, I used to talk a lot to different males etc and they take chatting and caring as being a come on, thats men for you, they take a while to settle into being alone after being in a relationship, they are looking to be looked after but that passes in time for most men.
Now I suggest that you say how much you want to help but in no way do you want a relationship ( that is unless you do) You will have to be firm and even suggest things he can do to occupy himself and maybe meet some one suitable, make it very clear how happy you are and you do not want those sort of advances, being blunt in a nice way is the only way otherwise you will string him along and it could get worse. Good luck