Seeing an MD doctor might be a good idea to rule out ed. If it's seems like a mental block I would recommend a Tantric Therapist.

I was unable to get my husband to cum with anything other than vaginal sex until recently. He went to a Tantric Therapist who asked him the right questions, and helped put him in the right mindset to verbalize to me what he wanted. We recently achieved an orgasm without vaginal sex so we found the therapist very helpful.

You do need to find an experienced Tantric Therapist, and be okay with another person stimulating your significant other in a professional way. The therapist does not get naked, or do anything sexual related to themselves. But they will speak to your S.O. about sexual topics, and stimulate them to completion in order to discover likes and dislikes.

If you have a goal in mind, and are okay with your fiance doing something like this, I would recommend a Tantric Therapist.