Nope, not at all.
I actually welcome competition for my pairings, as weird as that may be. In the past, I was a massive PokeShipper and one of my favourite episodes of Pokemon was Misty Meets Her Match. For me, Rudy was not an obstacle. His presence only heighten Ash's feelings for Misty and I believed Ash was jealous.
Wow, I was such a kid to think Ash had romantic feelings for anyone.
This doesn't just apply to Pokemon, but I often pair characters with more than one person (even my OTPs). Although, I wouldn't call myself a multishipper because, for the most part, I tend to believe there is one person they belong with; their true love if you will. But then, I do quite enjoy the many assortments of crushes, friendships and other relationships that they may or may not have - serious or otherwise. All of which are quite shippable (um, not sure if that's the right word).
I just feel a lot of the times, most shippers are so protective of their ships that they see every other person as a threat. Now, I'm not saying all of them operate on a "if they can't have him or her, then no one can" mentality, but there are an odd few that do. Believe me, I've been chewed out over stuff like this before. It's kind of scary how some shippers want certain characters to "GTFO" or "die in a hole" simply for having any sort of interation with one half of their ship. I wish they would understand writers bring in new characters for a reason, and if said character is a potental love interest, then it's usually to spice up the show and cause conflict for the popular couple of the show. It's a typical plot device, not an intention to screw over a shipping. OK, so I'm definitely not talking about Pokemon here, but that always bugged me. Again, not every shipper is like this. I know I'm not.
Also, why must everyone be paired up with someone? There are many characters I really couldn't care less about, let alone the ins-and-outs of their love lives. Lastly, if I ship two characters together, it is because I like them together. Not for the petty reason of leading them away from my desired pairing.