I suck at guitar, i've been playing a six stringer for about 9 months or so, with 2 years of bass before that.

I suck at putting two parts of a structure together without it sounding crappy and forced.

I also refuse to spend more than a few minutes on a song, once it gets to a point where i'm sitting there trying to theorise ideas like a musical jigsaw, i become the musician i do not want to be.

Is it because i'm not thinking in terms of a band or do i just suck?

I used to have somewhat of the same problem you had when I first started playing. I would sit down to learn a song and get bored with it after 10 minutes or so, only learning some parts of the song, like a bridge or certain part of the solo, or other parts that I could play and still sounded cool.

Eventually when you get better you'll be more willing and you'll find it a lot easier to learn songs, whole songs. I can only advise that you just sit down and actually learn to play whole songs, and just keep drilling it into you, no matter how bored you get or think "I can already play this, why learn it?" Not only will it be more impressive to your friends, but you'll learn a lot more by trying to play a whole song, IE more advanced chord progressions, timings, soloing( and if you learn the solo and the scales to go along with them, you can work out your own). Plus, it's kind of embarrasing when a friend recognizes what you're playing, and asks "what about the [blank]? That's my favorite part", and you don't know what it is.

i mean my own songs, not covers.

When I come up with a song on guitar, usually all I'm thinking about is that particular part. But when I go to plop it all into Powertabs, that's when I add in the bass and extra parts.

I'm the same way. I hate trying to write songs. If a song takes more than 5 minutes to write then it gets to the point where it's ridiculous. I end up with very simplistic songs, but I always play them and then a few days later I'll just think of something cool to throw in to spruce things up a bit. The only song I've written that took more than 10 minutes for me to write was Masquerade Pt. 2 but that's only because that song drew me into it and I was obsessing over it for an hour or so.