BIG dilemma!!

So my husband is an only child, his parents have been married 40 + years...had their ups and downs for sure, but ultimately very in love! Last year, after a 2 year battle, my MIL passed away due to cancer. We were and still are heartbroken. She was one of the sweetest people I have EVER had the privilege to meet, I adored her. My DH was absolutely devastated. It was so incredibly sad. It has literally been 12 months since her passing. I am close to my FIL, in fact we are selling our home and me, my DH and our toddler son are moving in with him this summer because he has had a hard time with loneliness since his wife passed. Today he confided in me that a neighbor of his had been asking if he wants to go out to lunch, she is a widow and is his age (in their 70's) he says that he is interested in the companionship and that they have known each other for many years and have good conversation. He wants to have company when going to the movies, dinner, day trips etc. he asked me my opinion on this (I said that it's not as if they are going to be getting married, that a friendship and companionship seems a positive thing etc because I didn't feel it was appropriate to criticize his choices)  He then asked me to keep it private for now, whilst he figures out how to break this to my husband who will undoubtedly be VERY upset - it's only been a year and he is still struggling when it comes to dealing with his moms death. I am so torn, I don't want to have a secret from my husband but I know how difficult it was for my FIL to confide in me and I don't want to hurt him. What would you guys do in my situation?!