Hello Biko,
It depends on the context:
- If a girl tells her girlfriend to be aware that her spouse or boyfriend is fooling around,then it means he is cheating on her and being sexually unfaithful.
But in the context of your posted dialogue it could mean:
- being engaged in any playful activity that is marked by unrestrained youthful behavior whether going out for drinks ,picking up girls etc.
It refers generally to making fun while acting foolishly, irresponsibly and wasting time without aim.
- Doing things of little value or no importance like speaking humorously and telling jokes.
- "He is not a professional ,but he was fooling around with her computer in hopes of fixing it"
Here it means the person is working at random , acting silly and ineffectively.
-When children fool around on the other hand they are just playing with toys for example.