Many people focused on building their career view being in a romantic relationship as a time sink. Several entrepreneurs have told me that they don't have time for a relationship. To evaluate whether this is true, we need to look at the three possible relationship states pre-marriage.
1. In a Relationship. A relationship takes a lot of time. You may spend every weekend with your significant other and one or two days during the week. During much of that time you are 100% with the other person. Sometimes you are able to double book time by watching movies, buying groceries, washing dishes, etc. but mostly this is maybe 15-20 hours a week (sometimes much more) of time you'd otherwise have free. (Obviously the "maintenance level," as they say, of the significant other affects time commitment.)
2. Single and Looking. You're dating around, or sleeping around. You're going on first dates, trying to impress, and following up on leads. (Using your preferred CRM system, no doubt.) You'd like to be in a relationship so you spend a bunch of time thinking about your ideal mate, comparing and contrasting the various folks you're meeting, and pining wistfully for the relationship of old or idealizing the relationship you someday dream of having.
3. Single and Not Looking. If you're not trying to go on dates and you're content being single, you'll have tons of free time. Weeknights and weekends are yours, and you profit from the power of low expectations.
My thesis is that In a Relationship is just as much of a time and energy sink as Single and Looking. There are various reasons, but one big one. With Single and Looking there's a great deal of emotional energy spent contemplating your lack of dating success, there's stress around existing dates, and of course, wondering, "Is she interested? Am I interested? Do I play like I'm interested?" You spend a lot of cycles thinking about your dating life even when you're not going on dates. The energy spent for In a Relationship, by contrast, tends to be concentrated to the time you're actually spending with the person. There's more certainty, less general / random anxiety and wondering. Easier to focus on work when you are working. So even though the "scheduled time" for a boyfriend or girlfriend is greater, the total energy commitment is about equal to the single but looking person.
Single and Not Looking is the best for those who want as much as time as possible for professional projects. Emotional wonderings are minimal since you're expecting to be single anyway. This is sustainable for a few years or so, or for lots of smaller chunks, but ultimately not a realistic long-term option unless you cut off your penis.
Bottom Line: Being single and looking takes just as much time and energy as being in a relatively low-maintenance relationship.
(thanks to Andy McKenzie for helping brainstorm this.)