[MMF] My first unexpected bisexual threesome

Please excuse the grammar as I’m typing this on my phone. This is a true story about this past weekend with my girlfriend and her good male friend. I identify as a straight male, very masculine and have only ever dated women. I’ve had experiences in the past in threesomes and orgy’s but have never done anything sexual with a man, until this weekend that is.
My girl and I rented a cabin in the mountains for the long weekend. It’s been a year since we’ve gotten away and we just wanted to get away from the stresses of work and kids. One of her male friends from college was going to come up for the day and hang out with us. We’ll call him Dan for the purposes of this story. About an hour after we checked in I heard a knock at the door. I opened the door and greeted Dan with a firm handshake. He was a pretty tall guy, I would guess about 6’5 and 200-230 (same as me with a few inches in height). My girl squealed and ran over to lay a big hug on him. We all talked for a while, they caught up and I got to know him better. I had always heard stories about him from college but never anything romantic.
The night carried on and Dan went to his car to get some things that he had for my girl Kate. He came back carrying gifts, a large bong and a bag of weed. Kate and I didn’t smoke too much weed but we decided that we would partake with him since he did offer. About 4 good hits later and everyone was feeling good, very relaxed and a bit amorous. I hadn’t seen Kate high before, but apparently it cranks her libido into overdrive. She proceeded to tell me how turned on she was and what she intended to do to me later; I was really digging high Kate. It was getting late and we invited Dan to stay the night since he was high as a kite and wasn’t in any shape to drive.
This particular cabin had a four person hot tub that Kate and I intended to take full advantage of later that evening. After we finished our dinner we all decided to head for the hot tub. Kate invited Dan to come out and soak with us. I was a little perturbed as I wanted to get freaky with my girl. Dan started stripping off his cloths right in front of us and we followed suit. Dan was in pretty good shape and was packing some serious lumber. I’ve always had a thing for cocks, just looking at them, and Dan didn’t disappoint. I would say he was 7-8 inches and thick. We ran outside and jumped in the hot tub since it was 18 degrees.
The conversation flowed and we continued to partake in the super strong weed that Dan brought. We continued to hit on the bong and eventually all of our heads were swimming. Kate started feeling around under the water where she found my cock hard as a rock. I felt her slowly begin to stroke it under the water which drove me crazy. I’ve always had a bit of an exhibitionist streak so I was enjoying the covert action under the bubbles. I could tell that Dan knew what was happening but he kept it to himself until I was almost ready to cum. He glanced over at Kate and asked if she intended to leave him out of the action? Kate has always been a bit vanilla and a proclaim monogamist so it surprised me that her good friend would hit on her. I was right on the edge and his comment pushed me to the point of no return. I felt my balls tighten as I stood up to cum. In an instant move Dan moved to our side of the hot tub and took my cock into his mouth. I was in complete shock but it was too late. I came so hard filling his mouth with ropes of hot cum. He swallowed most of it but some ran out of his mouth and down his chin.
I stood there with my cock in Dan’s hands and my jaw on the floor. Kate was shocked a bit too, but she wasn’t surprised. She failed to tell me that Dan was bisexual bordering on full on gay. We both took exception to his violation of our trust without even asking. He smiled as he wiped the cum from his face and quickly apologized. He said that he was so turned on that he couldn’t resist taking my load. Kate told him that it was not okay and that I wasn’t bi. To be honest I didn’t hate it but would have liked to known what he was going to do before he did it. That ended our evening in the hot tub as we all retreated to the warmth of the cabin. The weed had made us all so tired that we all passed out rather quickly.