My friendships feel like they're depleating

Okay well I didn't know another section to post this in but here we go

first I'll startwith what I think is a cause, I think it's because I spend more time with my girlfriend than I do with friends.

So now for the story and all the facts about my various relationships and how I feel about them then you guys can give me feedback or advice to go from here on. Some names have been changed.

Well eversince kindergarden this group of friends of mine has composed of about 4 or 5 of us who have always been pretty good friends, one of us in particular smoked since like 8th grade has smoked weed, then in the 10th grade we all hopped on (11th grade now). But this kid, Jon, was experianced and ever since then has been the "stoner" of the group, he'll come in later. In past years/months we have Always hung out together about once a weekend, now we only do 2, maybe, 3 times a month but were never all together cept for rarly. And latley they seem to be going to stuff sometimes without mentioning to call me also, assuming I'm doing something with my girlfriend whom none of them will talk to minus Jon.

Which leads me to my girlfriend, name her Sarah, we have been going out for 7 months now and love one another, (call it teenage love if you wish but at least to us it's love) I was her first kiss as well as her first time, as was she to me on the ladder. But it's things like this that mAke me seem to doubt this love, she knows I smoke sometimes, but doesn't like it and tells me not to tell her when I'm high and stuff, so I do t. Though latley me and Jon give rides to one another to school and in the recent most weeks have smoked together alot in the mornings, well Sarah is completley oblivious to this and I don't tell her 1. Cause she will get pissed and 2. Because she told me not to tell her. But at the same time I feel very guilty and feel like I'm doing it behind her back. Also now I hang out with her every weekend and if I miss one she becomes PISSED, and due to a result of this I have had to ditch my friends a few times which is why I think they don. Hang with me as often as before.

Now for two more subjects losley related, with Jon I used to not be great great buddies with him but now we are really a helluva lot closer, but he also is friends with another group of people "clique if you will," of the stoners and partiers and all that, so now oftenly we will smoke some of them up and they will to us and we'll have a jolly good time, now with the boys of this group who are all stoners I get alon pretty well, but around all the girls I get awkward and quiet and I'm sure they all think I'm a loser which I don't really mind but would prefer not to be. I just wanna be friends with them, but none of them seem to think the same. And also, I'm not much of a partier, mainly because me and Sarah would be doing something and I know Sarah would get mad if I ditched her or even told her that's where I wanted to go.
So I guess this isn't so much friendship problems, but how could I let Sarah be more flexible and/or acceptable of me doing what I like to do?

Tl;dr? I feel like my gf who I love is kinda holding me back and i don't know what to do.