Your nature may be just one that does not allow for a casual attitude. If you think this is you and your disposition there is nothing wrong with that. If you think this is due to a larger problem such as anxiety then you should then you should consult with a therapist. It is okay to even see a therapist just to process issues that are going on in your life. In the meantime, you can pursue some self help targeted at empowering yourself. Sometimes all decisions are impacted less by mental health problems and more commonly how we feel about ourselves. The confidence issues are able to dictate most of your major decisions.
In regard to the sexual decision pending, just be sure you are doing this for your own enjoyment and not to please someone else. Sometimes when we are not comfortable with some aspect of a situation it is because we deep down don't want to do this. This decision can be based on what would make him happy. If you can't imagine him engaging in equivalent behavior then you should consider that now.
I would suggest addressing your disposition by enlarging your knowledge of yourself and addressing your fears. There is a great resource in the Self Esteem Workbook. You can find a therapist on the site for the American Counseling Association
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