Accepted
.
And I believe the mental strength you are referring to is a psychological trait called 'Hardiness' which is defined by its presence as opposed to its absence (Meaning you can never have negative hardiness, some people are more hardy than others but that doesn't mean the others are weaker).
Also consider this, what, through subjective context, is the distinction between calling some people 'Mentally strong' and others 'Mentally weak' than calling some people 'Mentally blunt' and others 'Mentally acute'? In other words what is to say that these people feel pain more intensely than you when they break up? And it's not your strength so much as your lack of emotional response to the situation that makes you not give in?