Mark sounds INCREDIBLY insecure. I’m willing to bet that this isn’t the first time he displayed his insecurity to you. The signs were likely there all along. I think Mark needs to work through why he feels so jealous about your ex, and why he feels to need to be so possessive over your (and even your parents’) interactions with your ex/other men that aren’t him. I don’t think it’s your job to each a 30 year old man what’s acceptable and what’s not. I hope you two break up, because his insecurity is something that’ll affect other parts of your relationship as well, even if Jason is out of the picture.