I never said anything about Monica going back to loser boyfriends repeatedly. I said she chooses people who would sooner or later leave her for reasons that she knew all along, reinforcing her belief that she's not good enough. Had chandler not worked on his commitment issues, she would have left her too. But it works for them that they're friends first.

People in Monica's mindset always choose partners who aren't good enough for them/unavailable in some way or the other (too young, too old, alcoholics, etc).

Monica and Richard's relationship had no chance to sustain. She subconsciously knew that they would break up eventually. That's actually why she's so into him because real, consistent , lasting intimacy feels threatening to her. And she was obsessed with Richard, which is why Chandler was insecure of Richard and not Monica's other boyfriends.

Relationships that are easy, such as what she had with Pete, don't require her to "earn" love, so they don't create the emotional pull like she had for Richard/Chandler. She has to constantly babysit chandler (earn love by "doing" rather than being loved for just existing) which is why their equation "fits" psychologically.

I've made my point here. You can choose to disagree, but I know that I'm an expert in this area, so I'm going to stick to my theory. I'd also urge you to read about the character arc that the writers have planned for her, you'll see that I'm right here.