This story begins with the episode The Crossing. Rossi has been out of retirement and back at the BAU for 5 months. Hotch and Rossi are sent out of state to assist in a possible domestic violence murder.
..."Well we have four failed marriages between us. That should make us experts in something" said Hotch.
Hotch and Rossi were eating take out and discussing Hotch's marriage falling apart. Both men were a bit uneasy working together without the team. Although Rossi was a perfect replacement for Gideon, both he and Hotch shared a secret that they had an unspoken pact never to speak about. But there was a question that had been eating at Hotch since Rossi left the BAU ten years ago.
"Dave, I shouldn't bring this up..."
Dave had a feeling of what was coming. "Hotch, don't go there" he thought to himself.
Hotch continued..."but it has gnawing at me for years, especially since you've come back. Was I the reason you left the BAU?"
"That's a tough question to answer Aaron. I had just published my second book and it was successful. My publishers were after me to write and tour full time."
Hotch interrupted him "are you saying that what happened between us, didn't enter into your decision?"
"I'd be lying if I said it didn't. I knew you were going somewhere in the BAU, I didn't want to take that away from you. Besides you were engaged to Hayle. I guess I just didn't want to muddy the waters. I was probably going to retire within a few years anyway."
After an awkward silence, they refocused on the case, which was clearly a domestic violence situation. Maybe the husband had not hit his wife, but he controlled every aspect of her life and made her feel like a nothing.
Since the elephant was in the room anyway, Dave cleared his throat and asked "Aaron, do you ever think about what happened between us that night?"
"It was just one kiss. You said it yourself that night, we just wrapped up the Scarles Dale Skinner case, hands down one of the most horrific cases we had ever worked on. The things we saw... we just needed comforting...and we found it in each other."
"Absolutely" Dave said, trying to convince himself.
They continued to pore over the case files.
"But Dave..." Rossi lifted his head to look at Hotch. "Yeah I think about it."
"Me too. But we have to push it out of our minds. I'm not gay, I really like women."
"Neither am I" Hotch quickly responded.
"Before our kiss, I never had those inclinations towards another guy. I haven't had them since."
"I feel the same way" Hotch replied.
"Aaron, I worried that things would be awkward between us when I made the decision to come back. I never wanted to make you uncomfortable. I like working in the BAU again. And you are the unit chief. Some things are best left in the past."
"I agree. I was a bit nervous when Straus told me you were coming out of retirement. But for the record I'm happy to have you back. You are one of the best profilers the BAU has ever seen. Besides that, I value your friendship."
Hotch and Rossi finished the case and headed back to the BAU. After both men made the decision to leave their kiss in the past, they tried to go on as before. They continued to solve cases and work closely together. Neither man spoke of the kiss again, but there was an underlying chemistry between the two men.