Relationship is an investment

• If you invest in being an asshole, expect to get the returns from that.
• If you don't invest at all, or very little into a certain relationship, the returns will be little to none as well.
• If a relationship gives you big returns with very little investment, that's what you should invest in, not in the once that requires a lot of investing with very little return.
• Some stocks gain value over time, some lose value over time, this applies to you as well: if you have nothing valuable to offer, people won't invest in you and in that situation you are screwed if you haven't invested in anything in the past.
• Other people decide the value of your investment in them, much like you decide the value of their investment in you. Think this like the currency (Dollars, pounds, euros, rupees, dinars) you are using to buy the stocks; no matter how much you yourself value your contribution, it might mean nothing to the person receiving it. Many people would rather accept $1500 than 1500 in fish. You have to offer what other people want, not what you want to get rid of or what you have to lying around. 
• Some investment targets are inherently shitty, if you have invested in a shitty stock, stop investing more, it will only add to your losses. Accept the current losses, and move on.
• Past investments do not have better returns if the market has more to offer. If the loser you stopped investing in becomes successful, your investment in the past is still there, sure, but it won't gain more value on the market, quite the opposite because the market now has more to offer, and other people might and probably have invested more into the relationship with this person. i.e. People want this person's company, thus invest in it; They enjoy his/her company. Get it? Company, investment, stocks, market? In short: your past investment will only get you a smile and a "Hi." when this person walk right past you to attend something that is more meaningful to him/her. Which is more that people with no investment get, but still.. This is what stringing along, having people in reserve and treating them as your nth option gets you. You get to feel as important, as they once did. You get returns from your investments.

If you don't build or invest in meaningful relationships, you'll be left with meaningless relationships. And that is exactly what they are once you run out of things to offer, or when people wants/needs change overtime.

Another example would be a car (a mode of transportation on a road trip called 'Life'):
Investing in a sports car might get you attention, it goes very fast, but it also consumes a lot of energy, it has very little room for anything else, it can be annoyingly noisy, it really doesn't like bumps on the road, you really can't explore with it; you can only use it on roads traveled by everyone else, it requires a lot of attention; it's high maintenance and it cannot be maintained on your own, might get stolen or scratched out of sheer jealousy. You really can't let it out of your sight.
Also going fast isn't really a positive quality, since trip will over sooner. It is really more trouble than worth if you look past its superficial charm, it's an expensive way to have stress and unnecessary limits in your life.
If you decide to get one, and then realize it was a mistake; you have less capital to invest in a better, more reliable one: so you might only afford to get a used one which might be a good model, but with a shitty previous owner.

So don't get a car to impress everyone else, get something that impresses you. 
Get something that you actually need/want. Something that can handle bumps on the road, is enjoyable to drive, is reliable, can go off the beaten path, has some extra room for your stuff, has air conditioning so you don't suffocate when things get hot, requires very little maintenance, benefits from attention, but doesn't extensively require it, doesn't draw too much attention, is affordable and doesn't consume all of your resources.

Oh, in case I lost you; this whole car thing was a metaphor for a personal relationship with another person. (Pretty much any type of relationship, not just a romantic one)

Bear in mind that you are as much of a car or a company on the market to other people as other people are to you. i.e. when you are investing in a good and a reliable car, the other person might not see you as one.