I personally didn't read anything into you calling him 'the boy'. If you meant it scathingly, you were in an emotional moment of processing your feelings.
Most likely, your boyfriend found it as awkward as you did. He's in the middle, because he doesn't want to make his date uncomfortable by being overly demonstrative with you and doesn't want to hurt you by being overly demonstrative with him.
Either the guy is an Alpha Male and was purposefully saying little things to make you jealous, or he lacks a sensitivity bone.
Either way, you're probably better off not being too involved with him if being around him makes your feelings worse. Better yet, you could say something at the time - i.e. after the tuna comment, you could have said "a little discretion please, gentlemen..." If he is the game playing type, it should call him on it.
I once had a girl who made my girlfriend extremely jealous on purpose. I either overlooked it or didn't see it at first. I knew that I felt so awkward in the middle of them, trying to keep both happy. My girlfriend and I actually used to hide our affection in front of secondary partners, to make them feel more comfortable. We realised that this made it worse. Now I am very free around my girlfriend in front of secondary partners. Behaving in a normal way around her seems to help curb any games new people might play. Maybe I'm picking different types of people.... but all I know is when we weren't openly affectionate, the girls would play games... now that we are openly affectionate, the girls don't play games. Perhaps there's something to be said for showing a solid front. If they can't see cracks, they don't try to stick a crowbar in there?
I wouldn't badmouth this guy to your partner, but if he asks what you thought of him, you can always be honest and say you felt he was trying to get at you, but you could have just been reading him the wrong way.
And yes, you should definitely communicate your feelings. You shouldn't have to work through them alone. You both chose poly, your boyfriend is reaping the rewards - he has to pick up his end of the slack too. The slack being your feelings that result from his actions. Just because you're both open to sleeping with others, doesn't meant you have to be a robot. Especially since this is new.
In terms of the guy, some people try to push buttons and some people are just less sensitive than others. My girlfriend isn't very sensitive. For example, we were just on the phone this morning with her online sub boy (P), who will never be able to meet her. She slept with someone in 'real life' for the first time on Tuesday, also a sub boy. Probably not easy for him to hear. She declared to us on the phone "oh, I have a new method for training sub boys!" when neither of us responded, not wanting to hear the details, she repeated herself. P eventually meekly said "oh yeah?" to which she replied "yes! Before they get any pleasure, they have to learn how to please me!" Due to other things she'd told us earlier in the week, we immediately knew that this meant she'd taught him how to make her come with oral sex and then had sex with him as he reward. Lovely way for us to start the day.
We both went quiet and she couldn't understand why. Just lacks the tact bone. Or we have too many sensitive bones, who knows.
Sometimes things do slip out and people don't intend for them to.
You're still very new to poly and emotions do feel big at first. They still feel big for me too - I'm like you; less logic, more feeling. Be true to yourself and ask yourself what the root of the problem is. Are you scared he'll leave you? Are you scared he prefers this guy sexually? Are you mostly just angry because you felt your BF could have handled the meeting better? Once you know those things, have a chat with your boyfriend.
Good luck and let us know how you get on.