Male friend annoyances.....why bring along another friend?

Background: I (25) am married & my husband (24) & I are both friends with D (23). We all get along great, though D & I talk on a more regular basis than he & my husband even though he & my husband were friends for years first.

D & I have started to hang out a bit more lately. We both have pretty open schedules which my girlfriends do not! And we're bored!

The annoying part...Why is it that when we actually make plans in advance (not spur of the moment) to hang out he brings along another one of his guy friends w/o telling me. Why? I don't treat him any differently than my other guy (or girl) friends. I don't get it. Did I do something to freak him out? I have always been very friendly, thoughful & considerate to all my friends (& strangers!) but maybe he is reading into it as more? That was my only guess.

But I have been thinking that he has been showing a few signs of interest lately but I really couldn't know for sure. It's been a while! LOL He was hanging around me a lot at a recent family party we had, my mom even mentioned it to me. But I could be way off. Like I said, it's been a while!

It is just getting annoying, I wouldn't mind so much if I was actually friends with the other person but I'm not! I end up feeling like a third-wheel yet we were the ones that made plans. So annoying. Any insight from a male brain would be appreciated!
Thanks.

Sounds like he feels uncomfortable spending time with just you.

Why though? Because he's friends with my husband too?

You can't really be serious?

Obviously, he is attempting to avoid any appearance of impropriety. He is your HUSBAND'S friend. He is trying to protect that.

Sorry, I was serious. And that does make sense so thank you for that.

He's just really the only friend I can hang out with on a regular basis so I wish it was easier.

I think unless you are looking for trouble, you should find some girlfriends to hang out with.

I am not interested in him as more than a friend.

I have a few close girlfriends but they are always so busy. If it was easy to make more girlfriends I would love to. You don't know how much I miss girl time!