Exclusivity

So me and this guy that I've been with for 7 months and currently live together got into an argument about me hanging out with a guy friend of mine from work. He is upset that I hung out with him, but we aren't exclusive so both of us can do whatever we want according to him. So I go out with my friend and he completely freaks out. I know that we both have feelings for each other. He has really bad trust issues and I don't know how to resolve this. Pls helppp thanks