How can I help my fiancee get mental health treatment without making it seem forced? He needs help bad...

Eye to eye. It can help, when discussing it, to find things you mutually agree on that might benefit from consultation. Then approaching it curiously together, and perhaps offering to go with him, may be helpful. Also, there are some good websites that can help dispel certain myths about mental health treatment if that is applicable. Nami is good organization run by patients/"consumers" that provides info.
Getting help. As a psychiatrist I've noticed that people are often anxious to come to my office. The family pushing them is generally to no avail. If the patient has a good relationship with their primary care physician, that doctor is frequently helpful in expalining the basics of illness and why referral to a specialist is appropriate.
New ideas. As a primary care doctor, I point out that getting help from a therapist is similar to going to an orthopedist for a broken leg. You need someone who is an expert at the problem. Therapists can help him learn new ways of dealing with issues. You aren't trying to make him into a different person, just giving him a chance to feel better and more balanced. Remind him that you love him and support him.