I think that Jimmy has explained this:
Angela is his partner in crime, and although it is not explained what is he doing right this moment (or at least I don't remember that - it is irrelevant anyway), it seems that he can trust her enough to check on Fiona, his ex girlfriend.
If you remember, Jimmy was forced to abandon Fiona when he got in serious trouble with mafia - he was basically kidnapped without any chance to leave message to her. He is now too scared to just simply pop-up and say "hi" - while he might be still on the run from the mob (judging by his shady behavior), what he is really afraid is Fiona's reaction. But since he still has feeling for her (and he hopes that so does she), he has asked his "friend" Angela to check on Fiona, while he was trying to gather courage to show up in person. Coincidentally, Angela has managed to develop a small crush on Fiona as well, hence she might be doing this "checking" a tad too often...
This small plot goes really nowhere:
Angela tries to flirt with Fiona but is gently rejected, so she helps her instead to meet Jimmy/Steve/Jack. Fiona eventually rejects him as well. Both criminals disappear from the series.