Come on. You know it is, otherwise you wouldn't be asking this question. I think what you mean is more like: how can I find out if my partner has run up unmanageable debts? Money causes problems in a partnership when one or both over-spend, or when one or both hide the true facts of their financial situation.
Take courage, face your partner calmly and suggest you have a frank discussion about finances. Say that you feel tensions in the relationships are caused by this and you want to overcome them.
Money can make or destroy your relationship. Here are some tips to know if money is causing problem in your relationship.
You argue about money: if you and your partner argue about money every time, it is a sign that money is causing problem in your relationship.
Lack of transparency: if there is no transparency on your finances in your relationship it means monkey is causing or is about to cause a problem in your relationship. Be transparent about your income, expenses and do not hide necessary information from your partner.