I was going to say something like "is everyone taking crazy pills?", but I'll aim for a more serious response.

The problem is that people read way too much into what other people say. It sounds like you hear "partner? this person is clearly insensitive to the history of discrimination again LGBT people."

Instead try "I don't like the word partner, but it is a pretty standard term for not only the unmarried, but also married people. This guy probably doesn't understand it bothers me, but I'll give him the benefit that he meant no harm."