A lot depends on the people and the situation.
When I was working, and was friendly with some male colleagues, I might sometimes have lunch with one or other of them. No problem. It felt innocent to me and my husband wasn't worried at all. But my Dad found it very odd.
My husband has to work with female colleagues, which may include having lunch together or working away from home. I trust him, so that's ok.
But, as I indicated, before, if he told me that he was going on a long hike, alone in the countryside, with another woman, then I would not like it at all.
Of course, if ~ as in your case ~ this was something that had been happening long before I met him, then I really don't know how I would react.