A curious question...
This question was brought up in my own conceal-carry class. And, this is a question that should be resolved by a real lawyer, not by asking an internet forum. However, for a quick recap of the points we covered in CCW class...
People you talk to, and people you "confess" to as having just shot a guy, these people become potential witnesses that can testify against you in court. ("Mrs. Smith, isn't it true that, right after your husband gunned the victim down in cold blood, he called you and confessed that he just shot a guy?") (This example comes from my own carry-permit class...)
The only reason that I can possibly think of for not calling a spouse is that, in certain circumstances, the spousal immunity privilege to testimonial evidence might not apply. So, you must be careful to make sure that you don't create a witness that can be called to testify against you later.
Typically, married spouses share a privilege of confidentiality regarding communications made from one spouse to another. This old-fashioned common law rule was derrived from the concept that a wife was her husband's property, and therefore, a wife testifying against her husband would be like a husband being forced to testify against himself. The catch is, nowadays, wives are thought of (rightfully so) as independent people. So, the reasons for the spousal immunity privilege are slowly being degraded by the modern judicial system. Right now, for the spousal immunity privilege to apply (check local jurisdiction...) the people have to have actually been married at the time the communication was made.
So, if you shoot a guy, and you call your fiance, and she comes to your side, and then later you get married, then guess what? She can be called into court to give an account of the conversation between you and she when you called her for help! And, imagine what that phone call would be like! "Oh, (expletive deleted), Honey! I just shot some dude! Naw, naw... His brains are hanging out... I totally blew him away! No, I'm not scared... I'm fine... Yeah, I killed him... Just get down here, quick! I think I'm gonna be in trouble for this..." (Etc...etc...) The point is, you could potentially say some really damaging stuff.
I guess my advice is, (1) have a plan, (2) review your plan, and (3) when you need it, stick to the plan. This question relates to step no. (2). Talk to a lawyer about it, and make sure that what you propose to do in case of self-defense is really solid.