how to break up with boss on valentine's day

Just finished up an ER virtual internship at a boutique and my boss wants me to stay a bit longer to write up some reports. Its actually a full service boutique so they do the whole nine yards (M&A, capital raising, IPO, AM) and they wanted to build out an ER department so thats where I got thrown into.

I'm glad I got some finance experience but I'm now looking to get some IBD experience. Should I:

(a) Thank him for the experience but tell him I want to see how the IB industry works from a different angle. Hopefully get his blessing, and start looking for IBD opportunities at other boutiques through cold emailing (which is how I got this gig)

(b) Tell him that I applied saying I was interested in investment banking (true) and I don't really want to work in ER. Ask if I can get put on IBD deals instead - put more tactfully

(c) Drag out the ER internship while I solely focus on networking for BB/EB internship

stats:

feedback - did good work

relationship with boss - all through email so kind of non existant besides interview call

length - 3 mon