Strange thoughts about my relationship while taking Sertraline

I suffer from depression and anxiety (anxiety mostly) and 2 weeks ago I started taking Sertraline (50mg). The tablets seem to be helping with my personal anxiety, they are making me feel a bit spaced out and sick but I am having weird thoughts about my relationship and my mind won't allow me to decide if this is because of the medication or my worries are true feelings... My partner has many female friends, lots of them being ex girlfriends who he meets up with for coffee sometimes and stays in touch via Facebook, now usually this wouldn't be an issue but I am not used to it at all. My last relationship was for 8 years and I was never a jealous person, at all, most of my ex's female friends were mutual friends and it didn't bother me in the slightest. Now, in my new relationship, if a woman texts my partner I worry, really worry. There is one girl he met many many years ago on a dating site, they met once only but have kept in touch ever since and they speak several times a week, but he keeps this a secret from me which makes me very uneasy and worry even more. I think he keeps it secret as he knows it makes me feel uneasy (we have discussed it in the past but he said they are just friends). Anytime I am at home when I am meant to be at work - holidays or ill (daytime) she seems to be in contact (as well as another female friend) but never in the evening or weekends. I know this because she has called while we are in the car and his phone is linked to his laptop and a notification comes up when he receives a text. If he does answer the phone the first thing he says is 'I'm just with Jess.....' I can't help but feel uneasy about this and other situations replay in my head, my gut tells me it is strange and I can't shift the feeling.There are more things that have happened but too many small things to explain. He is the most loving boyfriend and I know he loves me very very much so why can't I just relax and get rid of this horrible feeling! I can't tell if I am really feeling like this or is it my medication making me think these things? I would really appreciate someone else's opinion, and please tell me if I am being silly.

Interesting that he keeps it as a secret. When something you say makes someone be secretive, it isn't really your fault. There is something wrong there, it is either his character that he is too sensitive and not sure of himself, or he has something to hide, and your questioning makes him wanna hide more. But what you are thinking about may not be what he is hiding at all, so be careful. You might not want to push him too much out of your life. Or you could be wanting power over the relationship like you used to with your ex. Anxiety can cause distorted view of the truth, you might be overreacting because you don't know her friends at all. You might feel left out. Maybe this was never what you wanted for yourself?? And you are blaming him for something else instead of making you feel like you are on your own. His being loving and all doesn't make much of a difference. Someone loving could cheat on you and keep loving you no matter what. But if he is an open person, and he is worrying about you, he might be afraid to make you sick or something. So, be open and honest with him, and not honest as in I am scared you are cheating on me. Be honest with him, don't make him hide things from you, if you establish deceitfulness into relationship, it will continue, and he might cheat on you later even if he didn't do it now, even if he is not considering it. Don't put thoughts into his mind. Don't be afraid to be abandoned. Take control of yourself. Not him! Don't force him into anything! Let go of this thought from your mind. Let go of cheating. Focus on yourself, and your relationship. If after a while being open and strong with yourself, if the nagging continues, it means you are not comfortable with him. Even if he is not cheating. It might mean this relationship is not good for you. Or you are not really honest at all. Anxiety and dishonesty is cause and effect. In my life, there are too many people who are lying to themselves, and not being honest with themselves, and I am caught in the middle of it. They are afraid of pain and weakness, and they are running from it. They are not even aware of how much they keep to themselves. So, don't run from your problems. Solve them. It is causing you too much grief. Be sure what you want. It is the most important thing. Be sure of everything. And don't believe in drugs too much. They are useless...

"because you don't know her friends at all." Sorry, I am confusing his and her. I meant his friends...