is it me or her?

So me and my gf have been together for almost 2 years now and we cant seem to stop arguing, latest one was about my work, we had talked the other day about having her going to some meeting and marketing (shes in marketing) on behalf of my company and she said yes but there was nothing really discussed on how we are going to go about it, it was lightly discussed, i wasn't sure she wanted to even do it. So a few days later my sister in law(shes not in marketing) came in and i asked her if she would be interested, she said maybe. I told my gf and she flipped and started saying that we already agreed upon it, that im in love with my sister in law, that i already made my decision and she wants nothing to do with it, that im immature and she cant be with me because of this, she starts cussing and saying disrespectful things ect.
Our fights seem to always happen this way and im wondering if its me disregarding her or is it her problem but i always seem to be at fault

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also I apologized to her already. but she refuses to apologize for the things that she said

Mixing business & pleasure is a bad idea. If you are going to do it you need to treat it like a business meeting. You needed to set a date & place. You need to establish the rate you were paying her & if you expected her to do this for free that should have been spelled out.

If this isn't the 1st time your GF has accused you of being in love with your SIL you need to examine your behavior & figure out why it's a recurring accusation.

Very very bad move with the sister and law. For me I have a sister- and its a MAJOR deal breaker if guy goes after her. That would basically end it with me.

wait what does this have to do with me going after my sister in law? Thats my brothers wife. No attraction there lol, but i think dalmom is right no business with pleasure. Thats the route im taking.

I have a question....why even bother asking the sister-in law if she wasn't in marketing in the first place? What was the purpose in that? I don't see any pleasure in any of this....just poor business practice.