My girlfriend is fantasizing about other people

Yesterday my girlfriend of 3 years admitted that she has been consistently having fantasies about other people for the past few months. Btw I am M20 she is F18. There are a few factors that lead to this, I want Reddits opinion on my situation and what shoul I do.

1. I work on a ship away from home. I have a month on, month off rotation so I'm often not home and can't physically please her.

2. My sex drive has been very low in the past few months. When I'm at shift we pretty much don't talk about sex or tease eachother or have sex by phone at all. When I come home we have passionate sex the first time we see eachother but after that I am usually not in the mood.

This has been going on for the bast 4 months. I was hoping that it would change when I changed companies because I was very nervous during the process of changing jobs but now that I'm here at the new place it's just continuing. I'm afraid it won't stop in the near future.

3. I may just be bad at sex. My peins is smaller than average and I cum very quickly so having piv is very doesn't last long. To compensate, I have learned how to finger her good but now our sexual live has basically come down to me fingering her which I feel is not enough.

She has expressed multiple times that she wants to be fucked for real. She also said that she has tried puting bigger things inside her and that it felt much better. She wants to have long and intimate piv sessions probably with someone bigger and I just can't give it to her.

And when you combine all of that, it's no wonder she is looking for someone else.

I told her I am glad she told me about that herself. I said that I will try to be more driven but that I can't promise anything since that stuff must come naturally.

I told her that it hurts me a lot to hear that but that I understand. For now the plan is to see how things turn out in the future and if it becomes really unbearable she is welcomed to leave. Btw I would not be okay with an open relationship.

What do you think I should do?