Why do some men/women get obsessed about a person they like?

You seem to be overly obsessed with this woman to the point that she will get a restraining order against you.
Stop this now because you are coming off as creepy, not caring and loving.

It’s an unhealthy relationship & he’s being overly possessive!!! IF you’re the HE in this relationship, I strongly suggest that you!! get some help!!! IF you’re the “SHE in this relationship, I suggest even MORE strongly that you rebuff him at every turn or request. I was married to an obsessive, abusive man & I can promise you that this is creepy & will only get WORSE!!! Since I’m not a trained professional & I don’t know of any on Fluther, I feel that the HE being discussed needs a trained professional to help him work through his problem!!!

If the male in question is a teen and the female is his first crush then it’s understandable. Hormones and confusing love with an obsession is common because it’s their first relationship and they may not quite understand how to express themselves or what is expected in a relationship. If its a grown man then there is a problem there. This is a person who wants to possess the female in question. Not a healthy relationship. People who are obsessed will eventually see flaws in the other person and rather than move on will try to get the person to become the version they built up in their head. Obsessed people live in a fantasy relationship.
The one thing I liked about my husband when we first met is that he saw my flaws as well but didn’t try to change me. Just like I saw his. I did get a little possessive and needy for a little bit but he put me in my place. I did get mad but eventually realized I wouldn’t like him to be clingy either. It really isn’t flattering when someone likes you for who they think you are and not who you really are.
It seems he is obsessed with her looks and weirdly her clothing as well. Could it be the guy is actually a trans and thinks this is his idea of the kind of woman he wants to be? Now there are people who are obsessed with just looks of their partner. And that is a recipe for disaster because he will dump her the moment she stop looking like his idea woman, because she can’t work out any more, or aging, or gained a few pounds or change her look to one he doesn’t appreciate.
By the way. Obsessed people often act like they are okay with family and friends at first to win the person over but the moment they believe the other person is dependent on them, they find reasons for you to drop friends and family. They know the easiest way to have complete control of their partner is to isolate them so they become dependent on them for everything.
I’ve seen that happen to people I know more than once.

Sex drive. Ba-BAM!

@Pandora Hi, actually it’s my bf I am talking about, and a woman of his past, I found out all of this, so it scares me that he is a narcissist or that he has some obsessive mental stalkerish issues.

What feels even weirder is that he has never acted this way with me, not wven at the beginning, he was somewhat like this but never how he was with her.

I am just scared that I am with a psychopath,He even took me 4 times to were she work and the had happened to met, because he worked there for some months, so obviously he has also talked to me about her, since we were dating, but I never realized how deep was his issue with her til further into our relationship he gave me more and more details about her.

Eject!

Insecurity. And a controlling personality.

The guy is dangerous, or potentially so.