Emotions and logic don't often talk to each other, and even more rarely agree. Your husband may be doing the best job he can to articulate his feelings. The first time my wife put a phone number of a play partner into her cell phone was something I noted as a step along the path. I wasn't jealous about it, but I recognized that from that point forward I could never know for my own self. I'd depend on my wife. I trust my wife absolutely, so it would never be an issue. In fact, I wouldn't even care if she spent an hour on the phone with a play partner and I didn't know it. But, I can understand your husband's view a bit here.
When you played in the threesome, it was both of you with the other guy. He was there. You were there. When you start chatting with other men without your husband, well...you're without your husband. It's different. Even though chatting is a very minor thing, and having a threesome is (physically) far closer a thing, the lack of togetherness on it probably bothered him.
That's not weird at all. Couples frequently do have disagreements on what is good for the goose being good for the gander and vice versa. This is especially true when it's an emotional issue. You may be fine with him chatting up the most recent play partner, but while logically he should be ok you doing the same, emotionally can be a very different story. Don't assume that if it makes sense logically, it makes sense emotionally.
You can. You're just learning something about how the two of you can swing together well. Honestly, I don't see this as all that serious based on what you've said so far. You're just learning what is and is not good for the two of you in swinging. Some couples play alone, some don't...for very similar reasons. Some couples are ok with their spouse flirting left and right, others not so much. Each couple has their own way of swinging. I think you just learned something about yours. If you're going to chat with others, invite your husband to join you. If he's not available, don't get into a chat program until he is.
If you haven't discussed boundaries in swinging in a few years, you're over due talking about boundaries by almost that length of time People change. My wife and I have changed many things in how we swing since we first started, and I expect we'll continue to change to maximize our pleasure and happiness in swinging.
It was your first time in an MFM. Some discussion about boundaries probably should have happened before. But, water under the bridge. Discuss it now.
The first time my wife and I had a threesome, we had a minor stumbling point (discussed afterwards) in that a few times I said "I love you" into her ear. I didn't get a response any of the times from her, and when it's just us I always do. I remember four times during the threesome. We talked about it, and she apologized and said she was very distracted. The sex was very, very good and it was a very distracting environment overall. The next day, she put a note in my lunch that said "I love you! I love you! I love you! I love you!" how cool is that? I love my wife
At any rate, you can't anticipate every possible thing that might happen in swinging and know how to respond. You're adding one or more other people to the mix, and they will act sometimes in unexpected ways. This is true for both of you too; you can act in ways you don't expect of yourself.
I remember the first time my wife and I got into swinging. We did a soft swap with a very nice couple that we clicked very well with. Great couple, great time, great experience. I didn't feel funny getting naked with a strange woman present. I didn't feel funny doing anything to her. I didn't feel funny when she gave me head. I _did_ feel funny when she put her hands on my side, near my hips at one point. Weird, huh? Couldn't have anticipated that.
So, you ran into something you didn't anticipate. No big deal. Pause, talk, work it out, go have more fun swinging. The important thing is to walk together in this.