There is a lot of baggage there.
Obviously his wife was his life long partner and I can imagine his feelings after having sex, possibly 20+ years with her.
He's not lonely for "sex" but intimacy in other ways.
It's entirely up to you whether or not you can wear the storm that is to come for a couple of years as that is how long it may take before he lets you in to his heart.
There is always someone else for someone whom has lost love. But, in death and the time that they were together, time is what is needed.
It would be a very arduous journey to travel but eventually, he would start coming across and forming a relationship however, as you have stated and him, his wife will forever be in his heart and home.
You need to consider yourself and be selfish in those thoughts before making any decisions from here.