"Well, animals do it!" is not an acceptable excuse for anything. We, as humans, are not animals. Some animals will also kill their own kind. Does that make it acceptable for humans to do the same? Even if you don't share my personal belief that God created us separate from and above animals, you should still know that it is not acceptable for us to act like them.
About love "not lasting," it depends on your definition of love. If you define love as "that tingling feeling in the pit on your stomach that you get when a someone attractive walks by" then you are right. Love doesn't last. However, I do not believe that that is what love really is, and I'm sure at least some people will agree with me. Love is a decision. When you meet the right person, you will begin to care deeply for them, on a whole new level than merely physical, mental, or emotional attraction. The most important thing is to make sure that this is the real thing and not just an infatuation. You need to really know the person before you decide to truly "love" them. (Truly knowing the person will keep you from being surprised when they turn out to be a slob.)
The thing is, when you make the decision to "love and to cherish, for better or for worse, through sickness and in health" and mean it, you will want to treat your partner with the respect, love, and admiration that they deserve, even when you're not feeling those butterflies in the pit of your stomach. You should put their needs before your own. This is difficult for many people to accept in the "me, me, me" society we live in. However, I'm not saying that you should just be a doormat for your partner to walk over, because if they truly love you, THEY will also treat YOU with the respect, love, and admiration that YOU deserve and will put YOUR needs before their own. And for me at least, getting treated that great by a person I was already attracted to would keep the romantic feelings alive as well.
So, in conclusion, true love is a mutual decision made by two people who care for and respect each other enough to be willing to sacrifice to give the other person the life and love that they deserve. I suppose the term could be "mutual self-sacrifice." I'd like to see an animal do that.