Has anyone experienced this😔

About a month ago these random thoughts came out of no where one night about my relationship me and my SO have been dating for about 4 years now, I love him so much literally more than anything us breaking up terrifies me and make me want to cry... I’ve always been a worrier and over thinker a “what if” thinker. the thoughts started off as “what if we’re not in love and just infatuated with eachother” and moved to “what if I’m falling out of love him” and then to “what if he’s getting bored of me” I literally couldn’t get them off of my mind I would go online and read forums and stuff constantly for a while I’d be ok bu then they’d come rushing back... it was so debilitating I couldn’t eat for almost a week I would cry all the time, I eventually went to the doctor and asked what she thought and she said it sounds like I have generalized anxiety disorder and recommended i should try CBT. The person hasn’t called me yet so idk what to do rn that was about about 2 weeks ago, last week it felt pretty much normal I saw him last Saturday and everything was normal I was so happy with him, we’re in somewhat of a LDR and only get to see eachother every 2 weeks so it sucks and is really painful but he’s worth all the pain and tears to me... a couple days after I had to leave the thoughts weren’t really bugging me but today they came flooding back and it’s all I could think about all day I was accusing him of being bored of me and I can’t shake the feeling that I’m losing feelings for him when I know I’m not bc just the thought of me losing feelings and breaking up with him makes me sick and want to cry..😢 I don’t know what to do.. has anyone experienced this before they just came out of ducking no where..ugh I hate them bc I know I love him I just want them to go away, my mom tells me it may just be my relationship changing which she said that it’s suppose to it can seem scary and make u think something is off but the relationship is just transition? Is this possible are u suppose to feel the same as when the relationship began? Could this be my anxiety? I just want these thoughts to go away. Yes I’ve talked to my bf and he’s so supportive😔❤️ I’m so blessed to have him he told me that he’ll be here no matter what and rhat he knows I love him just by the way I act and if I didn’t I wouldn’t be here.