My girlfriend says i've changed since the beginning of the relationship?

So context we've known each for a 3 years and we've been together one, made it official last year January. There is a bit of age gap her being 24. She says I've changed cause now she only sees me once or twice a month or every other month if she's lucky. Same for sex opposed to the twice a week it's now once or twice a month. I have explained that I am busy with work and I have responsibilities and i'm tired she says she gets that and she gets on top I don't mind. I started going down on her though I am a year out of practice since she was shy about the idea. I wanted a 3 sum for my birthday last month , she said no she isn't into girls and she's not open like that but I think I'm worth getting a 3sum. She brought it up yesterday saying how am I gonna handle two girls when I can't even manage one with my hurt leg. I hurt my let at work dropped a hammer on it. But she doesn't get it how it feels being in her and knowing ur the only guy that's been in there and i wanna see someone goingdown on her. Before sure it was fine I was more focused on getting her body use to me so yh I went at it for like hours we'd do it all day 4 to 6 rounds. Guess she got use to that for the first 4 months. Think I made a monster. I've told her if it's not enough we can both look into a guy and have some ground rules and she bawled her eyes out thinking I wanted to break up with her. I just want her to be happy and I think the whole monogamous relationship is unrealistic, not that I'm sleeping around, I have asked and she's shut it down. I just have more on plate and I don't know what she wants.

My girlfriend says i've changed since the beginning of the relationship?
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