I am very jealous person in general. That's not always a bad feeling, sometimes it's more admiring/motivational type of jealousy but it's still a feeling that tends to cause a lot of trouble, especially in a relationship.
I understand very well how bad and unfair it can feel, even if there actually was no reason to feel that way. I've been in similar situations and had similar feelings and it has been really hurtful so I tried to just ignore/push aside my feelings but that wasn't that successful and ended up feeling even worse in a long run. Lately, I've learned that it's ok to feel bad emotions and it's ok to think badly of someone else sometimes, negative feelings are also normal. Accepting them has helped me to actually process them and think through what may be causing them.
I don't deny, it is selfish to act and demand things solely because of those feelings but at least for me it has made it worse when I've gotten zero understanding to what I feel and why. Understanding and not pushing me harder down because of my "wrong feelings" would helped a lot in many situations, even tho it's not anyone else's than my job to process my emotions, traumas and problems etc.
I've been feeling very sad many times, because I've had a feeling that I'm not as important to my SO than his friends and I ended up feeling annoyed every time he mentioned doing something with them. Like I said, I'm very jealous person in general but I've never been the type of person who'd limit seeing friends or doing own stuff apart me and I never felt bad because of those things before. I have my own friends and own stuff to do also. I spent almost 24/7 of time with my ex and I never said to him that he weren't allowed to go and meet his friends alone, however his friends started to hate me because they thought that I had forbidden it. Well, in current relationship I do hardly anything together with my SO, we meet rarely even tho we don't live that far away each other. We almost never see each other's friends or family and I've been told by my SO countless times that this and that activity is just for friends or some other reasons that I find hard to understand. I can't help but feel totally left out of his life. I tried to be understanding, gave more space, pushed my feelings as far aside as I could so I wouldn't be so hurt all the time and because I didn't want to be that annoying, too clingy girlfriend who just cries and whines about her feelings because she doesn't get enough attention for her special princess needs (I'm starting to be a bit annoyed about the subject tbh, my apologies). Some time ago, I broke down pretty bad, not only because of this but this is one of the major reasons. I feel like I'm the only one who's trying to compromise (Idk if I am but I feel like it) and I've pushed my limits to a breaking point. I've realized that there might actually be 'right' to feel what I'm feeling now and it's not all for nothing and created by my over jealous mind.
I don't know if the OP is still somewhere around to read this, but if is or if there is someone else in similar situation, I'd suggest trying to somehow figure out and separate what emotion has logical connection to what and why and not to be too harsh on yourself or to other person in question. Communication is also super important, maybe try to explain your feelings to the other person without blaming them too much even if it's hard. You'll make through it, somehow. 
Edited by Pai, 15 October 2018 - 04:02 PM.