According to Theravadin Buddhism there are different stages of enlightenment. The first stage of enlightenment is termed Stream Enterer and the second stage, Once Returner. At these stages of enlightenment, a person can actually be married. There is also an example in the scriptures of a woman who was a Stream Enterer and had twenty children. That's a lot!
"Till death do us part", well, you are talking to a person who has a very good marriage and when I made the vow "till death do us part," I believed in it because I had a compatible partner and he has turned out to be a very compatible partner on the path, too.
The Buddha taught that in order to have a strong relationship, there are Four Qualities that should match. The four qualities are: Confidence or faith (going in a similar direction), Wisdom, Morality and Generosity. If these four qualities are matched then normally we will have a very harmonious relationship and are able to work out difficulties or problems along the way. The benefit of marriage is that it helps us make a certain amount of commitment, so that if things get difficult, we don't say immediately, "Oh, this is too difficult", and run away to another one so easily.
When you make that commitment, you are saying that are going to be there for each other in the difficult times as well as the good times. That you are going to try to develop unselfish emotions together, trying to work things out the best you can together, at least if you are on a spiritual path.
However, I don't believe all married couples should stay together, especially if there is abuse in the relationship. I believe it's not wise to continue a relationship where one partner is being abused and/or encouraged to believe things that are harmful.
So it really depends on the situation and the partnership whether I would agree with "till death do us part" because I wouldn't want a person to die from abuse in order to end the relationship. Actually, one of my very good friends lived with abuse for as long as Steve and I have been married, she is a similar age to me and a couple of years ago she called up to say she had finally left her husband because she was afraid she was going to get murdered. We had tried to encourage our friend to leave her husband quite early in the marriage because we could see what he was like. So we don't hold the concept that marriage is permanent and we have to stay with a relationship that is causing suffering.
We need to have enough Compassion for ourselves to know if the relationship is helpful or not. However some people use the Buddhist concepts to encourage defilements, "Oh, everything is impermanent therefore I am not going to make a commitment to you. It's your problem to have attachment to me." This is a wrong view and is not very compassionate. Many people have justified inappropriate moral behavior using this idea of impermanence. But the reality is that they are increasing their own delusion and increasing their bad Kamma by doing this.
As far as still dating, I don't see any reason not to, if you are not a monk or a nun and haven't taken on rules about celibacy. The Buddha gave appropriate teachings to people from all walks of life, lay people, monks and nuns, and he didn't put the concept of celibacy onto lay people or that we don't mix with other people in a romantic way.
Is this just increasing Dukkha? In the long run, if you have the goal of becoming fully enlightened in this life, then, perhaps getting married may be increasing Dukkha. It increases our challenges certainly, because we can't get everything that we want, but it can also be very rewarding. If we have a partner who is going in a similar direction we can act as spiritual friends to each other, which is especially helpful for Westerners who have to go back to a country where most people do not understand what they are doing. This is because there will be at least one other person who understands you, is going in a similar direction and can encourage you along the path. So it's not all Dukkha! Steve and I have helped each other through our relationship, and us being together has also benefited thousand of people around the world through our work as Dhamma teachers. So marriage can bring other benefits, too.