I've been on both sides of the UC weight gain/weight loss cycle and have 3 sizes of clothes in my closet from that.
You're faced with several whammies at the same time: UC itself, weight gain shame, separation from husband, emotional battering from same and more.
I don't know what caused my weight gain, it seemed gradual way back then, but because I have a supportive spouse the weight didn't bother me as much as UC symptoms. Then UC got worse and the weight went away. Personally I'd rather have the weight and be healthy but there was no choice involved. In later years I lost all the weight due to bad UC symptoms but am now in remission and weight is normal.
What should YOU do? IMO work on those things that are possible for you. Maybe see a therapist for the separation anxiety. Finding a support group for UC would help, oh yeah that's us
Most important is to take care of your health. When you get a grip on your UC things will seem brighter to you.
Exercise is a hotly debated topic here. My opinion is that moderate exercise to get blood flowing is good for my UC. I know what you mean about
the "need to dash" at any time. How about
doing a mall walk since there is always a restroom there, just stay near it. I like to do cardio on treadmill at the gym with Ipod music, again there's always a restroom near in a gym. Yoga is also a good source of calming as well as exercise and can be done at home. DVD's at your local library can show you how.
I know the anxiety, been there many times. Strangely I always felt comfort in thinking that if the meds didn't work I could always have surgery. There are so many here that have had good outcomes and back to normal life.
Diet. I have achieved remission because of changing my food consumption. Have you tried gluten-free and reducing carbohydrates? You might hit the jackpot with less weight along with fewer UC symptoms.
Best of luck.