Wow first of all thanks for all these reactions! The general conclusion seems very clear, that this is not going to work out in the end.
But I feel I have to explain a little bit more to some people calling me controlling or possessive.
Like I said, it was her who chased me in the beginning. She started texting me and wanted to hang out, initiate dates. I was single and I thought she was nice, intelligent and attractive. So our dates became more regular, until eventually we were seeing each other daily and started sleeping over and after about 6 weeks I asked her if she wanted to be boyfriend/girlfriend. She said yes.
I'm not very active on social media, but do have a profile and she wanted to be "FB official". So she put on her profile that she was in a relationship with me, and I accepted. So now on both our profiles it says 'in a relationship with...'. I thought that was cute.
Of course I then see all her other posts and noticed this guy's comments and her comments to him. It was quite obvious that for the last 10 months they were more than friends. (Not just the occasional hearts, but reacting in a way 'lovers' do, I think everyone here knows how that looks). Ok no problem, that was probably she had been dating or flirting with. I did find it a bit odd that this kept going on until now, also when we were already dating/together. But still no problem, I have no business in who and how she's talking to other people.
But then four months into our "official" relationship I see she is tagged in a picture on a night out with girlfriends drinking + that guy. That night already felt a bit 'off' as it was also for the first time ever she stopped responding to my texts or calls. We usually update each other a bit of how the evening is going or that we're home safe and wish each other goodnight etc. She disappeared until the next afternoon. That's when I asked her who she was out with last night? First it was just the girls and eventually she mentions him. He was a friend of one of her girlfriends. Then it was a mutual friend. When I told her it looks like they've been a bit closer than that by the way they communicate on FB, she admitted it was a guy she used to date a year ago, but it didn't work out, and eventually she said he was her on/off f**buddy until about a month before she met me. But that she already told him they can't meet 'like that' anymore.
I then asked her why she needed to be so secretive about still being in touch with him. We tell each other about all our other friends, male and female, even other exes, what's so different in this case? She said that she didn't tell me because I would only have been starting to ask questions, and that it would not me nice for me to hear about someone she had been sleeping with. And that I probably wouldn't like it if I knew she was hanging out with him drinking. I was a bit confused why you would do something that you think yourself your partner would not like, but still do it. And then stop communicating the rest of the evening as well? Asking about why they are stil calling each other sweetheart online and sending each other hearts and kisses, she said oh that's just how we communicate.
I told her it all feels a bit odd, especially because up until now we have been super transparent about basically everything.
Now, yes I have to admit at this point I started to put two and two together. Like someone else here pointed out, she's not a-sexual. She's been dating and sleeping around here and there for the past two years and that's perfectly fine, I think that's healthy behaviour at her age. But in our relationship she doesn't seem that into affection, and when we do have sex she sometimes completely switches off. For me that COULD be an indication that someone else is still on your mind. At least, for me that would be a good reason to feel a mental 'blockade' with intimacy if I'm still not over someone else. As much as I like the new person.
Then there's her still existing doubt if she has enjoyed her 'free time' enough. I asked her numerous times (also after this thing with the guy) if she would not rather be single again for a while? I would be sad, but if that's what she wants/needs that perfectly ok with me. I would never want to deny her any experiences she feels needs to have at her age. I know that feeling very well and it's an important and integral part of getting to know yourself and grow as a person. Not just sexual freedom, but also travel alone, meet new friends, explore different subcultures etc. Please do so if you feel that urge. But no. She's the one clinging on the idea of having a very serious relationship with me.
Now.. I have been in this exact situation in the past. A girlfriend who was a bit too friendly online with her gym instructor. Same thing. A bit too many heart emojjis, 'meeting' secretly, and when confronted the exact same story: That's just how we communicate, it's just friendly between us, he knows I'm with you, I don't want a relationship with him, we can talk really well, I didn't want to upset you. And guess what? That was a full blown affair behind my back.
So yes hearing all that again and not wanting to be taken for a fool another time, yes I picked up current gf's phone and copied the chat history with this guy to my email. And of course I find out they have been chit chatting all along the past four months. Meeting for coffees, calling each other darling, him texting her at 2:00am if she's still awake, her inviting him to come over for drinks with her girlfriends. The voice messages 'complaining' that I was asking questions about who he was, him responding 'oh I didn't know you were actually in a relationship with him' etc.
Now.. am I an overreacting asshole? Or is she just using me and still f*ing around?
What to make of her sending me a letter that she's incredibly sorry and had no idea how her actions upset me and she wants to do everything to make it work between us? Is that fake? Or sincere.
Oh and about another question here: she has no particular financial or other non romantic gain from being with me, other than that I pay the occasional meal and bought her some little gifts. I'm not some super rich old bloke or something.
Hope this clarifies a bit.