Just having a FOMO pity party

My SO and I have been together for almost 3 years (3 this February) and we've been living together since September of 2016. He's 21, I'm 22 and we are polar opposites which causes us to argue a lot but for some reason we can't leave each other alone. Marriage has been a sensitive topic for the past year or two because for the first year we were together he was all excited about the idea of us getting married and then I watched as he slowly starting to push back when he would propose. It went from "I'm putting a ring on your finger after we get our associates." And then when I realized a month before we graduated he had no intention of doing so and got upset he said "don't worry, we just have a lot going on and sometimes during the next two years for our bachelors I will be asking you to marry me." To "well after we get our bachelors." To "I want to wait until I get out of the police academy after graduation and have a secure job and a house." And he always makes dumb jokes about married couples being miserable and shit and I get a piece of paper saying we're married isn't everything to a relationship but it does mean a lot to me and to keep having it ripped away kind of hurts. I just would like to at least be engaged and have a really long engagement to wait for everything to be perfect but still have that "I want you forever" commitment. Anytime I bring up marriage now it turns into their big argument and I end up feeling guilty because I feel like I'm trying to force him into it and I definitely don't want him to propose before he's ready.

Anyway, today were coming back from the grocery store and he nonchalantly brings up that his younger brother was talking about proposing to his girlfriend when he came home from break and I just got instantly sad. It's not that I don't think his brother and his gf won't be great together because I really do think they will be and I'd be happy for them but it really twisted my heart because again it's his LITTLE brother who just turned 20 and has been with his girlfriend for 1.5 years. And my boyfriend mentioned this like it was the most natural thing in the world and of course they would be talking about getting engaged but anytime I bring up us getting engaged it's "omg we've only been together like 2 years this is too early to be talking about this." (He always thinks we've been together less time than we have).

And I get that each relationship is different and I shouldn't rush it but god damn I just feel really shitty right now and I don't really have anyone to vent to right now so I'm just going to do it on here. I'm assuming his brother wants to be married before he gets out on active duty which will be the spring of 2019 so I'll get to go to that wedding with my still boyfriend of 4.5 years. It also stings because I'm at that age where literally everyone around me is starting to get engaged and it's just feels like it's being rubbed in my face.

I guess I'm not really looking for advice or anything I just needed to get it off my chest and be a crazy girl for a second. Man this just fucking sucks.