LOOK FOR SIGNS OF JEALOUSY. If she displays jealousy or possesiveness over your time or relationships with others, it could indicate an unhealthy attachment. A respectful person should encourage u to maintain frienships and interest outside of your relationships.

ACCESS COMMUNICATION. Healthy communication is the key. If she avoids discussing serious topics or becomes defensive when you express concerns, it might be a sign of deeper issues.

Really

Trust your instincts, (but do not overtrust it so as not to make you decide any rash decisions)

SEEK HELP FROM OTHERS. Its worth condering your friends opinion about your fianc, BUT DO NOT BELIEVE THEM JUST YET, INVESTIGATE THEM YOURSELF.