When medications cause weight gain is it possible to lose weight if you cannot stop taking them?

Years ago I was on methadone through a methadone clinic and heard rumor that most females gained alot of weight while taking the methadone. After taking it for months I too ended up gaining over 50lbs. No matter what I did, not eat many calories or work out all the time, I never could lose more than 5 to 10 lbs. I finally just accepted the fact that to take the methadone I would be overweight. Years later, due to circumstances I couldn't control, I was taken off the methadone abruptly. Within 5 months I lost from 195 lbs down to 119 lbs. I stayed small for a couple of years until circumstances drove me to have to seek out suboxone/subutex therapy which is similar to methadone. With a year I was already gaining and now 2 years later I am at 174 lbs. I feel like it doesn't do much good to exercise or change my eating habits because it really doesn't make a huge difference in my weight. I feel certain that if I stopped the subutex that I would lose all this weight but if I stop the subutex I risk returning to a habit that was very bad for me. I recently found out my husband was signing up for online dating but he says he was just curious what kind of women would pick him but on one he described his ideal girl and one description was thin and muscular(like I used to be). He also occasionally looks at porn(I just found out by snooping) but he never wants to have sex with me. Now I feel I HAVE to lose this weight by any means! Is it at all possible to lose the weight while being on the subutex or do you guys think I should try to quit the medication so I can lose the weight? I hate being overweight and it really effects my self esteem and cause me to not want to go out in public so it would benefit me too to stop the medication. I just worry what negative effects it will have on me and our family if I can't control myself without the subutex. I don't know which is more important: stay on the medication and be overweight or stop it and be thin at a risk? Please help!!