First of all: be honest!
First part:
Do not cover for Carlos even when he insists. The next day, tell your wife you will call Williams. At the office, speak with Martha(?) and tell her you haven't met Carlos, and talk with Peter about every subject. Then, call Williams and tell him to wait until next week. Finally, before you leave the office, call the bank and talk to Nikki and invite her to the party (a little flirting is allowed

).
At the party, Susan shows up and she's quite pissed, but you can calm her down eventually. Leave with her.
Second part:
Meet Williams and politely refuse his offer (it's not my way of doing business). Call the bank: you'll find out that the loan wasn't accepted. Tell everything to Martha and Peter. When you go home (or at Peter's, it's the same), you'll meet Nikki. Drive her home but don't accept her invitation. At home, speak with your wife and explain everything (she won't trust at the beginning, tell her "c'mon, why would I lie to you?"), before the "intermezzo"...
Third part:
Go to the bank, (be quick now!) follow the "pissant", head for the elevator, use "violence" until he tells you that Williams is the guy who refused the loan. Tell everything to Peter, you'll decide to go to his office that night. At home, tell everything to your wife, then go with Peter but give up the plan and just return home ("we'll spy on him tomorrow")
Fourth part:
Spy on Williams (or meet him at his office, it's the same) you'll discover his little affair with Nikki. Pay her a visit and ask her for the tape. After her blah blah make sure she'll tell you she'll find someplace to hide.
Fifth part:
Make a copy of the tape, and call Peter on your way to the electornics shop. Then call Williams, ask for the money tell him you want them cash and hang up, then call your wife, tell her to hide herself for a while, then go to Peter's neighbour's garage, and then go to the fashion show to meet Williams. Ask Peter about everything (MOST IMPORTANT, THE CHUBBY LADY), then meet Williams, he won't give you the money, you insist on calling Capricho, (BE QUICK) when you see a choice called "Scream: Look Out!" click on it. If yiu are fast enough, you'll also have the chance to come up with a typical action movie line...
That's pretty much it. In fact, I think I did way too many things to finish the story (I mean, for instance, I'm not sure I had to make a copy of the tape).