Hummer it seems everyone who has posted has been through similar events that brought us to diving. I too lost a lot of weight - 50lbs. I ended a 12 year relationship. I decided to get into diving because back in 1974 or so I got interested in the scuba club, but never followed through for various reasons. Doing scuba diving is for me!
As for a man not wanting a woman for a buddy, I have my DM cert and it is funny to me that men take on the role of protector. Part of it is just gentlemanly politeness, but part of it is "I'll take care of you". I am not knocking them, it is just the way it is. I don't get all up in their face I just know that push come to shove you'll be glad I'm there. Buddies are there for each other. Trust me if someone is taking the advance class they are there to learn thus they do not know everything.
As for the class and diving in general, I try to visualize the dive. I go from start to finish - do I have all my gear, have I assembled everything, checked connections, breathed my regs, buddy check, in the water bubble checks, decend, dive, buoyancy, ascend, 3 minute stop, exit, review. Navigational will come to you once you have done it a few times. It is not as mysterious and difficult as circumnavigation with a sextant!
Good luck and remember to breath and relax.