At best, it suggests a person who does not take the marital commitment seriously. When we add the fact the he did not disclose this information at the onset, it strongly suggests deception as a character trait. Between the two traits, betrayal and deception, we have a picture that does not bode well for intimate relationships. And when you believe that he will be different with you, you are probably engaging in self-deception. You are getting involved with someone of whom you will always be suspicious.
Intimate relationships are difficult enough.
We do not have to add to the difficulty by staying involved with someone who has already displayed less than admirable character traits. The last issue is more difficult. You are in love. Even, if as you yourself suggested, you know that you should leave him, you are afraid of the pain involved. You're caught between a rock and a hard place.