A guy said i care about you in the broad sense. does he mean i care about you a lot?

Not necessarily. He could mean he cares about you the way a girl cares about her best friend, it doesn't particularly mean he cares about you in a romantic way. If you're still feeling confused, try asking him exactly what he meant, letting him know how this sudden statement has puzzled you.

Thanks - But he is my ex so I'm really confused. Also I am English and he is American and sometimes considering we speak the same language we do say things and terms that confuse the other!

Well maybe you should sit down and talk to him about it, ask him how he really feels about you, and in what sense did he mean "I care about you"