Being in multiple relationships is not an issue and so is maintaining them. However, what is unknown is the effect it could possibly have on the psychological well-being of an individual.
Love itself involves a lot of psychology and the brain is well engaged in the whole process. There is actually a connection that puts all of you together during the whole thing.
When in a relationship, people get to be psychologically attached to each other and almost behave in the same manner albeit unknowingly.
If a person can easily be connected to the other in a relationship, guess what the effect will be when that person is in multiple relationships with people spotting different characters?
The effect could be so huge as the psychological aspect of their being and the general make up will be crumbled.
They may not understand themselves and this could be disastrous to those who are particularly so emotional around everyone they meet and fall for.
The individual may completely be detached from the real world and end up spending most of their time in the fantasy world.
The effect comes gradually and is so consuming that whoever is going through it does not get to actually understand themselves.
Besides that, being in multiple relationships also means you have to spot a new figure and personality everytime you meet those you are perceived to be in love with.
It is highly unlikely that they all have similar preferences and is therefore impossible that you maintain a single personality throughout. You will live a fake life and you can never be yourself.
Besides that, you may also lose your sense of thought and be resigned to doing what they like. You will lose the important control over yourself and your free will also be in question.