Question: Does it matter to you how many times your significant other has had sex with other people (read: not you)? Well, does it? If you've been with over twenty partners does that mean anything, if your current lover has taken only one or two? It's an old question to which there are no definitive answers, only opinions.
That said, how many sexual partners are too many? There can be too many cooks in the kitchen, right? So why not too many cocks in the boudoir?