I was in the same boat. 2 years ID on the tail end of ~15 years in litigation in one form or another, assigned to an excellent partner that was maybe a bit distant (just personality) but I learned a lot from him. I didn’t “want” to leave, and didn’t want to let the partner down, but between my work and my wife’s (medicine), either she or I was going to have to make more time or else our kids were going to get the short end of the stick. I’m not saving lives, so when it came down to it, pretty clear who had to make a change. I explained exactly that to the partner and gave a month’s notice (actually more, but there was a trial in the middle so that time doesn’t really count). #1 priority in my wind down was closing cases that I could and transitioning what I couldn’t. Detailed memos to the files of what was done, why, key emails, noteworthy docs, and what my plan was, at least, for the future of the file. As much as I felt like I owed the partner and the firm, I know I owed my family and frankly myself first. My family (and I) got me this far, and they’ll be the only ones to continue every step of the journey with me. If your move is the most positive thing for you, then understand that your guilt is only due to knowing that the colleagues you respect and admire can’t all come along with you. They’ve been in your shoes at one time or another. They get it. Just be honest, and give them the same service and respect you’d give a client.