Stammering is not necessarily related to nervousness or shyness. In fact your stammering partner may stammer more with you because he or she feels they can 'let their hair down' with you, be him or herself with you. You may recognise that several of the above situations can be difficult even if you don't stammer. But someone who stammers may be especially concerned at these times about how people will react to their stammering and may be feeling a strong internal pressure to be or appear 'fluent'. It has been known for people who stammer to put off getting married because they are anxious about saying their vows.
Many people find they stammer more when they are ill or tired.
Some people find they stammer less in those circumstances. How you can help. You or your partner may wish to handle such things differently on different occasions. be prepared to talk and keep talking about stammering with your partner. What you can do is to listen and acknowledge that it is important to your partner. The more you listen to your partner the more you will understand as time goes on.