Thank you for patience - this is the first I've been made aware of your post - no idea why it didn't show up sooner, but it's very possible the California power company (PG&E) shutting power down to a million people (I'm one of them) had something to do with it. This computer has been running off a cell phone for 3 days now - and it's not a reliable internet connection whatsoever
Now, with regard to your husband's overly friendly nature and this widowed woman from his past:
First - most men (truly, the vast majority) aren't likely to cheat if all of their affections and interactions occur right in front of you. What you have to worry about is anything he makes secretive. So the phone calls and kisses on cheeks are certainly overt, but most likely innocent and certainly nothing more than what he shows right in front of you.
Second - I understand your concerns about this long-time "friend", newly widowed; however, if he had any inclinations toward her in a romantic way - he wouldn't have married YOU, he'd have pursued her or waited patiently for her to be available.
Her saying, "I love you" could be something she's said to him "as a friend" for most or all of the years she's known him. Many people say this in a platonic way. We can love someone and not want to marry them or have sex with them. This woman may say it to her female friends as well. Sort of like those people who call even strangers, "Darlin'" or "Honey", etc..
Once more - that he conducts these calls right in front of you not only should reassure YOU that it's innocent, but it could be that he does it in order for you to make sure it STAYS innocent.
All this said - calmly tell him how you feel without saying it in the same way you have before which triggers him to get upset.
In order to change a response that's the same every time - you need to change the way you approach it.
Perhaps start by asking him if he'd be suspicious or uncomfortable if you were chatting in depth with a male friend from your past
By encouraging him in a gentle way to look at this from a more personal point of view (his seeing it happen TO him rather than your seeing it happen to YOU) - may be the perspective necessary for his having an "AHA! moment"