No it's not typical and it's a huge red flag. Do not marry him unless this is sorted out- it will not get better. There is nothing you can do to help except support him in seeking professional help. First, an honest conversation with his doctor and a thorough exam to check for physical issues. Could be hormonal, thyroid etc. Then he needs a therapist to sort this out. This is reddit so I can't make any conclusions. Could be anything from hormonal issues, to trauma, or he's uncertain about his sexual orientation. If he values your relationship he will seek help.