Just off the cuff, it sounds like your free testosterone levels are too low. If this were the case, it wouldn't mean you lack testosterone; rather, it woulc mean not enough of your testosterone is in the free state in the blood, and free testosterone is needed both to achieve erections AND to feel yourself being "in the mood."
Wellbutrin is a compound which affects the brain chemicals dopamine and norepinephrine instead of serotonin like other antidepressants. Even though Wellbutrin is supposed to be lower in sexual side effects than serotonin controlling drugs, the studies have still shown something like 22% of Wellbutrin people have sexual problems. You might be among that 22%, and this would result from the fact we are all genetically unique from one another.
Now, before you try anything I'm about to suggest, talk to your physician and, perhaps, to other physicians who can help guide you because suicidal thoughts are clearly dangerous and nothing to be taken lightly.
Having said that, you may want to (with the help of those practitioners) investigate a more natural lifestyle. St. John's Wort is an herb which is used in some situations to promote mental stability, and it is virtually side-effect free.
Cutting out junk food with trans fats (hydrogenated and partially hydrogenated oils), reducing saturated fats, and turning to more natural extra virgin olive oils would be one step in the right direction.
Being sure you have plenty of fresh fruits and vegetables in your diet (5-6 servings daily), and introducing a daily exercise plan (if you don't already have one) would be more areas on which to focus.
Reducing meat products by eliminating beef and pork (unless you're one who has blood type O -- type O's seem to be able to tolerate land-based animals better than the rest of us), cutting down on chicken, and adding in a little fish here and there (cod, perhaps) is another area which can help. Also, keep protein serving sizes to about 4 oz. per day (roughly the size of the palm of your hand).
Organic foods can also help you by eliminating most of the chemical pollutants found in conventionally produced foods. You wouldn't believe the toxic metals and hormones found in these more conventional methods, and it's truly amazing what proper diet can do to make a person feel really good!
Beyond that, you might just have over stimulated yourself in the past reaching a point of mental "conditioning" whereby your brain doesn't think of sex occuring in the "normal" way. Instead, it thinks of sex as related to naked photos and / or the computer.
Best of luck to you! Hopefully something from this can help, and remember to discuss with your doctors any of these changes you wish to make before you start making them.