I think major sensitive nipples is the worst of it, they came and went for me but were worst in the second half. Some people find their milk dries up, but I didn't. Also finding tandem feeding a challenge at the moment from a practical pov while feeding DS to sleep as DD needs feeding constantly in the evening, but that will get better.
I was feeding my 6mo when I fell pregnant again and I had to stop as my boobs were so painful. Luckily she has always been an eating machine so didn't cause any problems and I actually found it quite a relief in the end as I could concentrate on the pregnancy more rather than stressing about milk supply.
I know exactly what you mean - think you need to make a decision so you can stop gradually if that's the case. I have had to change DS's routine because I'm feeding DD and feeling guilty about that, I think he would feel pushed out if I stopped entirely 'because' of her iyswim?
I fed my baby (16mo)through very horrid morning sickness until I was about 18 weeks pregnant. Just felt the right time to stop, fed other children for a year and 18months, so no definite pattern for me. Sensitive nipples came and went . Ironically even though I was being so sick I still enjoyed feeding the baby...