My boyfriend tells me he's not the jealous type... and he's really not. He happens to be very open and if I didn't want a serious relationship he would have been okay with that.
Lucky for him I don't want anyone else to have him
But I think this situation is a person-to-person basis. I'm sure there are plenty of guys out there who are just looking for a good time and couldn't care less who you decided to have a "relationship". There are the guys that are simply so infatuated with you that no man can come within 50 ft of you. And then there are some guys who just want you to do what's best for you. (and those are the good kind!!)
Assuming you trust this man or whomever, I would have to take his word. If he freaks out, well, quite frankly it's his own damn problem because he told you it was alright. Most of the men I know don't dance around these sort of issues. If he's going to lie to you about this, then he isn't worth having anyway
Hope this helped!