I just feel like to loneliest person to have ever existed

My boyfriend is currently at a party that i left early (I’m sick right now) and where he told me he would join me in bed in a couple of minutes because “without me it’s just not as much fun”. Also he knows that i don’t feel very good about being alone when I’m sick. It’s now almost two hours later. I just don’t know how to trust him right now. Yesterday we got into a huge fight over a female neighbor living next door to us (we live in a student home). I’ve had a pretty bad feeling about her for a while now because she is quite mean to me everytime it’s the two of us but as soon as my boyfriend enters the situation she is all of a sudden all smiles and friendly. I’ve very specifically told him that i feel uneasy about her and he assured me that he feels the same. Still, everytime they meet (which is almost daily because they both do volleyball with a couple of other people around the dorm) he mentions her at least a couple of times during the next conversations with me. I’ve said to him that i would wish him not to talk about her as much which he is trying to respect. Now yesterday it got a little out of hand because I came in on them casually chatting and her inviting him over for her dinner party. She said I could also come but she never talked directly to me even though I was walking right through the room. After this I kinda freaked and told him that i would really not like him going there because i feel like she is kind of disrespectful towards me and I felt like she was constantly flirting with him. He told me he wouldnt go. In the night I apologized for making such a big deal out of it and told him that i was simply worried. He said it was fine and that i was probably taking everything a little more seriously than usually because I’m sick.
Now tonight because I felt really lonely and kind of got trust issues I went through his phone (i know this is bad on my side and I feel really horrible about it) but then I found out they were actually texting yesterday afternoon and night. She texted him first, again inviting him for dinner and again mentioning I could join. He told her he wouldn’t be able to make it but was very friendly and still kept up some small talk with her.
When I read this i just got really sick to my stomach. I know it might sound like not much of a deal but the fact that he didn’t tell me about her texting him when we specifically talked about her like an hour before just feels very disrespectful to me. What I feel worst about is the fact that i actually apologized for my concerns.
I know that she is most probably at the party tonight too and it just makes me feel like the loneliest person that has ever existed.