Are They Emotionally Unavailable? 5 Warning Signs to Protect Yourself

Emotional availability is a crucial yet underappreciated aspect of healthy, successful relationships.
Emotional availability describes the ability to sustain emotional bonds in relationships. - Healthline
Although a partnership may persist, it cannot really prosper unless both people are able to be vulnerable in this way.
But how does someone know if they are emotionally available?
And how can they find out before investing years of their life in something that isn't likely to succeed?