Notice that I said relationship, not marriage. That’s a completely different beast to tame. For whatever reason, today’s generation seems to favor cohabiting over actually tying the knot. As high as the divorce rate in America is I can completely understand why, even though I am in favor of marriage. Any large financial commitments should be kept separate until there is a concrete commitment to the relationship.
When you're not married there is nothing binding you together besides the fact that you “love” one another. Let’s say you and him/her have been living the dream relationship for the past couple of years, but him/her was a starving artist with little financial support to offer. No problem! You're in love so you take on the burden. Then one morning Lil Jodie wakes up and decides he/she doesn't love you anymore. You've wasted more than just your time.
By splitting expenses you’re helping both of you reap the benefits of being in a relationship by relieving any excessive pressure from either side. Depending heavily on one person financially can put a burden on a relationship if money isn't plentiful. That could lead to issues in other areas of the relationship.
There is absolutely nothing wrong with spoiling your partner if you're financially able to do so, but most of us at this age aren't well off enough to do so without any concern. You remove any ulterior motive and get to see if that person is really there for you. It’s not uncommon for people to stick around in relationships because of the perks, but love is about giving not receiving. No one should ask for anything they aren't willing to give. Relationships just tend to work better when equal partners carry their own weight, but to each his own.