Jealousy is killing me

A little over a month ago I started dating a girl. I am 21 and have never been in a relationship. She is 19 and she went out with about 4 other boys when she was 14ish, although I am her first boyfriend she has had within 4 years.

The thing is she grew up mainly around men, her parents divorced and she mainly stayed with her dad and two brothers so she is rather "tomboyish". Because of the way she grew up she now has quite a few more guy friends than girl friends which of course me being her boyfriend makes me nervous.

We use to work the same shift where we worked, which I loved because we were always around each other and made sure we kept each other out of trouble. I guess management got wind of our relationship and moved her to overnights. Now there is this other guy that works overnight that seemed to of taken interest in her, to the point of even jokingly mentioning we should break up. She tells me she has no interest in him, all though every time she calls me during her lunch break I can hear them talking to each other, which I found extremely rude in the first place considering she was calling me.

It is just killing me. I tried telling her I don't like all of the guy friends she has and all of the guys she talks with but she just overreacts. I know it is probably just me. I don't know exactly how relationships work out, this being my first, I cant help but think If I don't keep her happy all of the time she is going to immediately jump ship for some other guy. I want her to be happy but I also want to talk to her about whats going on but I'm pretty sure it will just make her angry and annoyed with me.

This happened with my last girlfriend, almost an identical situation.

We started dating and life was great. She started talking to this guy we work with a lot because they got along very well and had similar humor. 2 months later she tells me she has a crush on him, a month later she breaks up with me because she doesn't know what she wants.

I am a strong believer in NOT telling a partner what to do, they should know what will piss you off and how not to behave. You need to make your concerns known, and by known I mean straight up tell her that you don't like what is going on and that you are very uncomfortable about it. Don't dance around this one, you need to be crystal clear immediately.

This may come across as an aggressive approach, but you don't want to let this fester, it will hurt ten times more if this guy comes between you.

Edit: If she gets heated with you and your simply telling her it makes you nervous or uncomfortable thats a red flag. She should be understanding, it doesn't mean she should immediately do this or that, but she should want to listen to you and hear your concerns.

Don't concern yourself with making sure shes happy all day everyday. Its your natural instinct being your first relationship, but you will stress you and her out if thats what you are always trying to do. Happiness is half you and half her, remember that.

Careful with how you put it though ... jealousy can push someone further away, especially when she feels you should trust her word.