There are some questions you should ask yourself. A few might be:
-Are you looking for a long term relationship?
-Do you want to raise children?
-Do you want a partner who will be there for you when you need them?
-How do you handle stress?
One committed relationship is hard work. HARD work. Adding another person at least doubles the stress and effort. When they fight, you have to deal with the effects on your partner(s). When you want attention, they won't be able to give it because they're already spent.
In my experience, the other two fought so often that my male partner was on edge and couldn't handle any problems between us. He didn't have the energy to give to both of us (and he has a lot of energy). She and I also had to work out our own issues without putting him in the middle. Very frustrating to not be able to vent to your partner. I got to the point where I wanted more, I wanted that love, I wanted the real deal, not pretend, temporary, or okay for that year.
Maybe sex outside of a relationship some people are willing to tolerate. Adding a real relationship is a whole other thing. WHOLE other, nothing like easy sex or a friend they have sex with.
A lot of people don't know what they can handle. The woman involved in my situation told our partner that if he fell in love with someone she would be happy for him, she had no idea that she wouldn't be, just like I had no idea I'd hit a wall and want something more than what I was able to have in that group of three.
Yes, different people can handle different things. Take it slow and try to find out about yourself before getting involved under those conditions. If you learn before getting too deeply involved you could be saving yourself a tremendous amount of heartache, pain, and loss. It isn't something a person has to do to know. It's about a person knowing themselves enough to make that decision.
Sorry, I have a lot to say. I went through a lot of pain, my boyfriend went through a lot of pain, as did our ex. I hope some of it is of help.
Take care of yourself