Advice: IBD analyst - can i become friends with a client?

I'm an IBD analyst and around 4 weeks ago we had a PE fund invite us to listen to a proposal for us to be their financial adviser for a possible transaction.

During their presentation, I really got on well with one of their team members. I'm an analyst and he was a senior associate so he's a little bit older but not too much. We spoke a lot throughout the meeting, I was asking a lot of questions and it wasn't just in a formal way as we were having banter together and we got on very well, it was like we were good mates meeting for a catch up even though we just met. Even my MD made jokes after the meeting like "you two were best mates in there, we're worried they might hire you ha". I also really like the PE funds strategy, a niche area and a big interest of mine so i really want to become friends with him not only from getting on well but more importantly through a network perspective as i want to go down the PE route and feel he could be a good contact to have.

However I didn't send any follow-up emails and we never spoke since that meeting 4 weeks ago, I didn't think I would need to send a follow up because I figured we would take them on as a client and I would see him again and could build the relationship throughout the project and then after months of working together we'd naturally grab each others phone number and stay in touch. However, my plan failed because my MD decided he didn't like the project and declined them the other day. My bank also has a strict hierarchy so if my seniors ever found out me, an analyst, emailed a client without their consent I'd get in trouble.

Now I dont know what to do. I really got on with this guy so i kind of want to become friends with him and he works in the area i want to exit into which would be great from a netwroking perspective, but i can't exactly approach him now its been 4 weeks he's probably forgotton who i am and it will be awkward to send a follow up 4 weeks later, especially now we've rejected them and if i did approach him he might think its because i want to network with him for a job. Also if my team find out they might think im trying to exit too. Any advice?