I had a 6 year relationship. It had its ups and downs, good times and not so good times. I would like to know how old you are?
If you're still in your 20s, I would prefer casual dating over serious relationships. I have actually always liked it better, as I always seemed to be more stress free and care free when just casually dating around. But I guess part of "growing up" a lot of times is getting serious with that person that you're in a relationship with and some of us get there sooner and others take their sweet time. It's all really up to you to decide, and trying to do what truly makes you happy regardless what others might think is the key.
Like some others have mentioned, a lot of people grow up with expectations to get "serious" and eventually get married and what not. Hell, a lot of people probably only get married because they are "expected to" get married. It's almost as if they're thinking "uhhh, yeahh, of course i'm gonna get married, are you crazy" and if you really dig deep down you can find solid reasons for both being single and being married. But not that many folks are willing to stand out and simply say to them selves "ok, I'm more happy single and spinning plates, life is just less complicated".
Now, every now and then, there will come that one girl that's gonna make you wanna settle down a bit, that's what happened with all my "relationships". The one that lasted 6 years, she was fine as f*ck, but also bit of a drama queen and so into her self that I dont' think she will ever be truly happy. Her attitude left a lot to be desired, and it just got frustrating the last few years, as things will get to you over time. Resentment is a big killer of relationships and pretty much you want to work out your problems as much as possible and not just ignore them thinking you can "live with it" as eventually you get so sick of sh*t that you can't control it anymore and it becomes very clear that you are just fed up with it. This is why it's always best to work out your bigger issues right away and see if they can be solved before years and years of the same pattern eventually just becomes too much for you to deal with.
I'm a pretty damn easy going person, and dont' worry about a whole lot usually, but my last year with the ex I found my self going off on her and yelling at her for stupid things that really just got built up over time. I would later sit and think "man, why the hell did I blow up like that" and I knew that I just wasn't happy anymore, but it was hard to just get out because of being together so long, so it was a drawn out process where we grew apart. I know she was fed up with some of my sh*t as well, as she would have her own blow ups over what I percieved was "stupid sh*t", and we just seemed to piss each other off. After we were over, she was actually trying to get back with me for the longest time, but at this point I really had an epic run going with "running game" and picking up girls, so I had no true interest of going back to her and I am proud of my self for not getting suckered back into it. I knew DEEP DOWN that long term I would not be happy with this woman. She may have been fine and a lot of guys may be interested, but anyone spending life with her will have a lot of drama a bullcrap to put up with that I just don't think is really worth it man.
Ironically, my current 9 month relationship is also far from perfect, lol, but i'm not saying this to scare you at all. I have had good experiences in a relationship, but you just have to realize that unless you get married and spend the rest of your life with her, most relationships eventually come to an end. And realizing and accepting the fact that it could and probably will be over some day, will help you deal with things a little better and be more reasonable about the expectations and also will help you put your self first (which ironically will make her more into you and make her wanna stick around more lol).
The only problem with "spinning plates" is that sometimes you start to get that feeling that you're missing that "special someone" in your life, as most of your friends may have LTRs and be married and what not, so every now and then you will start feeling like "hmmm, it would be kinda nice to just have that one special girl". You just have to try to remember that feeling when you are with her though, as a lot of times you simply want what you can't have. Married guys wish they were single, single guys wish they had someone lol, seems to always work like that. I always try to remind my self of how I felt while either single or with someone. This way when you have little fights and what not, you can keep things in perspective.
I think experience will teach you what makes you happy and what doesn't. If I just had to give you a direct answer, I would say, if you're in your 20s still, keep spinning plates. You will eventually find some girls that you're just gonna end up in relationships with, that's a given lol. I didn't plan on any of mines, as girls like to say "they just happened".